I used to play 1. d4 as White, and had a terrible record against the Benko Gambit (something like 20% win, 80% loss). It improved slightly to 30% win after I switched to the Qc2 line. I have since switched to 1.e4, hence I do not encounter Benko Gambit as White anymore.
Review: Benko Gambit as repertoire against 1. d4
I decided to play the Benko Gambit myself as Black, and it gave surprisingly good results. The plan for playing Benko Gambit is very simple, fianchetto the dark-square bishop, line up both rooks on the a & b files, and play on the Queen side. The dark-squared bishop is very powerful as it has an unobstructed diagonal. White will have a very hard time hanging on to his two a & b pawns. The only way you can lose (other than obvious blunders) is if White checkmates you first (which is not that easy to do). In endgames, it is almost always the case that Black has an advantage.
From online research, it is stated that most players who are below master level don’t know how to play properly against the Benko gambit. Due to the simple and standard plan, you can also move very fast without having to calculate much and hence that is why Benko gambit is very good for rapid or blitz games. On the other hand, playing White against Benko gambit is very hard and tedious, hence white players tend to either lose on time or make a blunder in time trouble.
My rapid game against a 2100+ rated Lichess player: https://lichess.org/Yflbsg5H/black#1.
White made a blunder by playing b3. What is the best move for black? (There is more than 1 correct answer.)
Best Books on Benko Gambit
This is a book by a Singaporean author, Junior Tay.
This book is by Grandmaster Sergey Kasparov, who shares the same name as the famous Garry Kasparov. (See also Garry Kasparov Masterclass Review.)