London system 2. Bf4 or 2. Nf3?

Is it correct to assume the general difference between 2. Bf4 and 2. Nf3 is that by starting with the knight you risk running in to a vast amount of openings that you have to know? But that you "conceal" your London intention for another move. Apart, of course, if you have a specfic line intended that just needs that specific move order.

2. Bf4 is largely considered to be the better because 2. Nf3 can lead to some lines where white is in a bit more unpleasent position.

However if you want to stay flexible and maybe go catalan or some other opening 2. Nf3 might be the way to go.

Yeah, it seems easier to walk in to other openings more easily with moves such as 2... Bg4 and 2... c5 and you might struggle to get the bishop out before e3.

2.Bf4 is played to avoid this line, when you cannot play Rb1 to protect the Pb2. White tries to be faster and to play Nf3 later.

It has nothing to do with concealing.  It all has to do with 1 line where Black pressures b2 and then causes problem with ...Bf5 after the Queen goes to c2 to cover b2.  The Bishop on f5 is hanging, but Black then gets ...Qxb2 and the a1-Rook cannot be saved.

I do not recall the exact line, or why the switch in move order prevents it, but that is the reason for 2.Bf4.

Note that the London System is bad against 1...g6 and slightly dubious against 1...f5 or 1...e6/2...f5.

It is best to only play the London against 1...d5 and 1...Nf6.

In the following videos the choice of 2.Bf4 vis-a-vis 2.Nf3 in the London System is discussed in detail.....(beginning at 3:05, of the first video)...

Introduction to the London System - Hanging Pawns

https://www.youtube.com/watch?v=S_OYdWbJMKM&list=PLssNbVBYrGcCjajrI7QtQi48nKOfy-W5O

Move Orders in the London System Part #2 | 2. Bf4 vs 2. Nf3 | How to choose the move order for you! - Chessimple...

https://www.youtube.com/watch?v=_bp3Oacqo7g

Basically, holding back on Nf3 saves white a tempo towards addressing black's quick attack on the queenside.

Nowadays, both move orders are perfectly viable and neither is objectively better than the other. This “refutation” where Black takes on b2 is perfectly sound for White, albeit a draw (see below). However, the London is a draw with best play anyways, so play on. I’d recommend the 2. Bf4 line as 2. Nf3 c5 is a NUISANCE.

1. d4 d5
2. Nf3 Nf6 (Bf4 c5)
3. Bf4 c5 (e3 Nc6)
4. e3 Nc6 (Nf3 Nf6)
5. Nbd2 Qb6 
6. dxc5 Qxb2 
7. Rb1 Qc3
8. Bb5 e6
9. 0-0 Be7
10. e4 0-0
11. e5 Nbd7 
12. Nb3 Qb4 
13. Nfd4 Nxd4
14. Nxd4 Qxc5
15. Re1 a6
16. Bd3 g6 

That line you posted scores better and imho is better than the line where White plays 2.Bf4 and e3, c3 Nbd2, etc.

1.d4 d5 2.Nf3 c5 is not a nuisance if White plays 3.c4 transposing most likely to QGA. I think 1.d4 d5 2.Bf4 c5 is worse line for White than 2.Nf3 c5, since Black usually gets an improved version of exchange Caro-Kann and scores much better:

Which opening is not a draw with best play....?

So 2,Nf3 is not a nuisance if you don't play the London System...

After some opening moves like 2.Nf3 c5 it's better to play something else. I don't think the London System should be played against everything.

4... Nc6 can be met by 5. Nf3!, delaying the c-pawn's development, as White gets a good game after 5... Bg4 6. c3 e6 7. h3 Bf5 8. Nbd2 Bd6 9. Bxd6 Qxd6 10. Nh4 Nf6 11. Nxf5 exf5 12. Qf3 g6 13. g4 and if 5... Bf5 then simply 6. c4 e6 and you can play 7. c5, 7. cxd5, or 7. Nc3 and you'll be slightly better no matter what, and Black likely won't be ready for any of it.

The best is no london system

It's improbable that Black will play this engine line that you gave. Black plays ...Bh5 instead of Bf5, which is just equal and is like a bad exchange Caro-Kann. If White continues with 8.Nbd2, Black plays Bd6 and White has nothing. And if 8.Qb3 Qd7 9.Nbd2 (9.Ne5 Nxe5 and ...Ne7) Bd6 is equal. If you have studied Caro-Kann seriously or some other openings with the Carlsbad structure, you should know you Black's play is easy. And Its probable that Black will be prepared to face this Nf3 line, since it's Black who has scored better in these lines.

I just started playing again and have been trying the London System, but that Bf4 just keep getting pushed back. There's nowhere to fallback to once the pawn is at e3. I can go Bg3, but they keep coming with their pawns and I have to trade bishop for pawn at some point or move a pawn to h3 to fallback to. Which doesn't seem to work out well.

The bishop might get pushed back in some some Indian systems and the Dutch. I think if you play 2.Bf4, it's good to transpose to Jobava London (London with Nc3) against some openings like the King's Indian. Here's how you might play after 1...Nf6 and ...g6.

If your opponent plays 1...d6 or 1...g6, it's better to play 2.e4 or 2.Nc3 and try to transpose to something like the Pirc/Jobava line with Bf4 and Qd2 like above if you want to play a Bf4 system.

2.Bf4 is the in-your-face I'm playing the London System, while 2.Nf3 lines can lead to more flexibility and transpositional lines.

Maybe the solution is to not play the london system at all. e4 praise hikaru