I’ve been trying to learn London System but is it good though? (I’m 900 Elo)
No! A 900 player should stick to the Ruy Lopez and Queen's Gambit from both sides.
They follow opening principles to the letter. At 900, Opening Principles are the answer, not opening theory.
Also, at the 900 level, you should be learning various pawn structures and patterns. Playing the London will basically stunt that critical concept. You need to learn diverse pawn structures, the concept of tension on the board and when to leave tension on the board and when to break that tension via an advance or a trade. Many beginners feel that if a White pawn is on c4 and a Black pawn is on d5, even if both are protected by other pieces in their army, that the must trade or advance immediately, often times when leaving the tension there is correct. You can learn this from the Ruy Lopez and Queen's Gambit, especially the latter. The London will stunt your growth in this area.
You also need to learn about various pawn structures, when color complexes come into play and when they don't, etc.
The London won't help you in these areas. Play the Ruy Lopez and Queen's Gambit from BOTH sides.
I’ve been trying to learn London System but is it good though? (I’m 900 Elo)