The guide to the Benko Gambit
I'm guessing that the author is Steffen Pedersen and the book is the Gambit Guide to the Benko Gambit. I don't know about the quality of the book but I would treat it as an introductory primer to the Benko at best. I'd make sure to be get a more recent book that covers options where white avoids allowing the Benko.

I like Finegold’s easy instructions and his sense of humor. I find Fedorowicz easiest to read. Alterman is the hardest to understand but he shares a lot of cool tricks and traps.

Look for a book that pays special attention to the 5 e3 lines and goes into depth with b5xa6. The 5 e3 line is the best chance White has for fighting for an advantage if you choose to decline the benko. 4 Qc2 and 4 cxb5 a6 5 f3 are only equal, yet there are a number of extremely strong (2700+ FIDE) rated GM's who have played 4 Qc2, and rather recently, too. 5 f3 (after 4 cxb5 a6) has not been played by any very strong players in quite awhile, but is still seen sometimes at lower ratings.
Note that 4 e3 is nowhere as good as 4 cxb5 a6 5 e3.
White pretty much has no other way to avoid the benko, as after 2...c5, there is no other reliable move besides 3 d5, as 3 Nf3 and 3 e3 don't over much of anything.

I have recently come into possession of the book, “The gambit guide to the benko gambit”. It was written in 1999 and I was wondering if it was still valid as I’m currently learning the benko. If anyone new anything about this topic would love to know. Thanks in advance!
the theory in the benko has not changed much, mainly due to how unpopular it is.

Look for a book that pays special attention to the 5 e3 lines and goes into depth with b5xa6. The 5 e3 line is the best chance White has for fighting for an advantage if you choose to decline the benko. 4 Qc2 and 4 cxb5 a6 5 f3 are only equal, yet there are a number of extremely strong (2700+ FIDE) rated GM's who have played 4 Qc2, and rather recently, too. 5 f3 (after 4 cxb5 a6) has not been played by any very strong players in quite awhile, but is still seen sometimes at lower ratings.
Note that 4 e3 is nowhere as good as 4 cxb5 a6 5 e3.
White pretty much has no other way to avoid the benko, as after 2...c5, there is no other reliable move besides 3 d5, as 3 Nf3 and 3 e3 don't over much of anything.
Id honestly say that the return variation and the fully accepted a4 lines are the most challenging. e3, Qc2, and the other options typically still give black plenty of play

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.
It's a misconception that old books especially openings aren't useful anymore. You aren't playing against NMs. Below NM, games are decided by mistakes, not by opening moves. The BG isn't dubious like the Latvian Gambit and Elephant Gambit.

There was a lot of back and forth from the 70’ to 90’s deciding if white or black was better. Black has the better endgame so don’t allow an early queen trade. GM Bologan used it to defend against much stronger players at Biel 2012 to no avail. But it says something about the gambit that he’d at least attempt it. There are some instructive games for white there too, see link.
https://www.chessgames.com/perl/chess.pl?tid=78291&pid=14216

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.
It's a misconception that old books especially openings aren't useful anymore. You aren't playing against NMs. Below NM, games are decided by mistakes, not by opening moves. The BG isn't dubious like the Latvian Gambit and Elephant Gambit.
the Bxa6 lines are actually a bit dubious compared to the other

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.
It's a misconception that old books especially openings aren't useful anymore. You aren't playing against NMs. Below NM, games are decided by mistakes, not by opening moves. The BG isn't dubious like the Latvian Gambit and Elephant Gambit.
the Bxa6 lines are actually a bit dubious compared to the other
A bit dubious is good enough. Ultimately the game will be decided by tactics, mistakes. The most important, the black player likes the position that arise. That is a victory psychologically.

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.
It's a misconception that old books especially openings aren't useful anymore. You aren't playing against NMs. Below NM, games are decided by mistakes, not by opening moves. The BG isn't dubious like the Latvian Gambit and Elephant Gambit.
the Bxa6 lines are actually a bit dubious compared to the other
A bit dubious is good enough. Ultimately the game will be decided by tactics, mistakes. The most important, the black player likes the position that arise. That is a victory psychologically.
maybe, but the issue is that if white knows what hes doing black is left cramped and simply down 1-2 pawns for nothing in return
lets look at the critical main line
black is down a couple pawns, cramped without much space to maneuver in, and has to follow a tight rope in order to not be completely losing
a better gameplan would be this
white never got the chance to play a4 while at the same time blacks pieces are better placed.

Thanks for all the input but if i were to read it, would there be lines that aren't valid anymore. as after all, it was written in 1999. Is there any point or should I stick with other sources. I have a short and sweet benko course on chessable and due to chessmoods 6th anniversary I watched the 4 hour benko course for free which was very useful. As a decent club player, I find the ideas in the benko give a very easy game for black, although I have only just started playing it.
It's a misconception that old books especially openings aren't useful anymore. You aren't playing against NMs. Below NM, games are decided by mistakes, not by opening moves. The BG isn't dubious like the Latvian Gambit and Elephant Gambit.
the Bxa6 lines are actually a bit dubious compared to the other
A bit dubious is good enough. Ultimately the game will be decided by tactics, mistakes. The most important, the black player likes the position that arise. That is a victory psychologically.
maybe, but the issue is that if white knows what hes doing black is left cramped and simply down 1-2 pawns for nothing in return
lets look at the critical main line
black is down a couple pawns, cramped without much space to maneuver in, and has to follow a tight rope in order to not be completely losing
a better gameplan would be this
white never got the chance to play a4 while at the same time blacks pieces are better placed.
8... Bxf1 is dubious. ...Qa5 is stronger, with the idea of either 9 Bd2...0-0 or 9...Bxf1 10 Kxf1 Qa6+ 11 Kg1 0-0 12 e5 Ng4 13 Bf4 d6 with compensation.
But 8...Qa5 9 Bd2 0-0 10 Be2 Qb4!? is very interesting, or 10 a4 Bxf1.
In the first variation board that you give, White is only up +0.32 after 17 Ra3, despite being two pawns up, so Black clearly has good compensation (I9 14900k CPU, Stockfish 20240107 single net dev build). I think 13 Ra3 right away, followed by either 14 Nd2, 14 Qc2 or 14 Re1 is a bit more testing for black.
*edit* looks like your second board variation transposes into the line I gave with a different move order.
I have recently come into possession of the book, “The gambit guide to the benko gambit”. It was written in 1999 and I was wondering if it was still valid as I’m currently learning the benko. If anyone new anything about this topic would love to know. Thanks in advance!