Mastering the Chess Openings Vol 2 vs A Strategic Chess Opening Repertoire for White? (by Watson)

Basically the title. What is the difference between these books? I'm looking for a book to improve my d4 knowledge.

Would you say the first is worth reading for beginner?

@3
"Would you say the first is worth reading for beginner?" ++ No.

The first is more generic.  Covers virtually all d4 openings.  Depth of each opening is sparse.  Think about it - you have 400 page books that cover the Classical King's Indian by itself.  Here, you might get 10 pages on the Classical KID.

The other is called a repertoire.  It gives a single line, maybe 2, against each possible defense.  It is specifically written for White, and let's just say, hypothetically, that it covers the Saemisch against the King's Indian.  It will not cover the Fianchetto, Classical, Four Pawns Attack, etc, because it is specifically written for White to simply have a repertoire with 1.d4.

There are 3 types of opening books:

1) Repertoires (most popular) - Coverage a line for each possibility by the opposing side.  Written specifically for 1 color.  Like a French book for Black might give the Classical, Open Tarrasch with 4...Qxd5, main line advance, and the symmetrical defense for the Exchange.  It will not cover the Closed Tarrasch or Winawer or McCutchen.

2) Broad Overviews - Books that try to cover everything at just the 10,000 foot level.  Watson does a decent job with his, but most of them are garbage (See "Standard Chess Openings" - Schiller)

3) Objective, theoretical works - These were popular in the 90s - most of the Batsford Books by John Nunn were this way.  They focus on a single line, but lay out all the theory in an objective manner.  All lines are covered and not skewed toward one side.  Examples: The Main Line King's Indian (Nunn and Burgess), The Pirc in Black and White (Vigus), Rubinstein Complex (Pliester), The Nimzo-Indian: 4.e3 (Hansen), The Main Line French: 3.Nc3 (Pedersen), etc.

Personally, I see it as follows:

Under 1600 - Learn Opening Concepts

1600 - 2400 - Have a repertoire handy for White - Learn all theory and multiple lines within the same opening for Black.  For example, a 1.e4 repertoire book or a 1.d4 repertoire book for White - I would suggest 2 or 3 of them and that way you can mix and match if you don't like a line, like 1 book may give the Fianchetto KID and the Catalan against QGD and NID whereas another may have Saemisch, Exchange QGD, and 4.e3 against the Nimzo.  Maybe you prefer the Catalan, but hate then Fianchetto KID.  Now what?  You could take the Catalan from one book and the Saemisch KID from the other. As Black, however, you study the theoretical works of your opening of interest.  Like in my case, I probably have over 20 books on the French Defense.

Over 2400 - You need to know extreme detail of every opening you play.

Nice, thank you for the elaborate answer!