Track down FM Nick Raptis. As he said: "I know the Reti 124 moves deep."
The biggest problem with that book is the theory is dated! Especially the 2...d4 line.
Also, you say some lines are not in the spirit of the Reti. You cannot force the Reti as White. If you are going to open 1.Nf3, the Reti can only occur if Black plays an early ...d5. If Black does not play ...d5, you do not have a Reti. If c4 is played and not d4 by White, you likely have an English (1.Nf3 c5 2.c4, 1.Nf3 Nf6 2.c4 g6 3.b3 Bg7 4.Bb2, 1.Nf3 Nf6 2.c4 e6 3.Nc3 is a direct transposition to the English Anti-Nimzo - 1.c4 Nf6 2.Nc3 e6 3.Nf3, 1.Nf3 Nf6 2.c4 c5 3.g3 b6 4.Bg2 Bb7 is the Hedgehog, etc). If d4 does get played, you likely have a transposition to a Catalan, Kings Indian, Slav, etc.
The Reti is not a great line for players under 2200 because A) you cannot force it, and B) the numerous numbers of transpositions to the English and QP openings.
The biggest problem with that book is the theory is dated! Especially the 2...d4 line.
Also, you say some lines are not in the spirit of the Reti. You cannot force the Reti as White. If you are going to open 1.Nf3, the Reti can only occur if Black plays an early ...d5. If Black does not play ...d5, you do not have a Reti. If c4 is played and not d4 by White, you likely have an English (1.Nf3 c5 2.c4, 1.Nf3 Nf6 2.c4 g6 3.b3 Bg7 4.Bb2, 1.Nf3 Nf6 2.c4 e6 3.Nc3 is a direct transposition to the English Anti-Nimzo - 1.c4 Nf6 2.Nc3 e6 3.Nf3, 1.Nf3 Nf6 2.c4 c5 3.g3 b6 4.Bg2 Bb7 is the Hedgehog, etc). If d4 does get played, you likely have a transposition to a Catalan, Kings Indian, Slav, etc.
The Reti is not a great line for players under 2200 because A) you cannot force it, and B) the numerous numbers of transpositions to the English and QP openings.
The OP is a 550 Blitz player. So the fact that the theory is dated wont matter.
Whats the best Reti opening book you can recommend? Best chess regards