Old school texty FIX is incredibly slow. FAST FIX is faster but not fun to use. Largely SBE has won adoption on the market data side, with huge platforms like Euronext (biggest on Europe) using it.

I stopped working in the area on the age of FAST FIX, which was extremely good for the time. Do you know what are the differences to SBE?

I guess I'm biased based on experience at the companies I've worked at but FAST never seemed to have good libraries or tooling

It was a proprietary messaging middleware library. We actually found even FAST FIX slow.

FAST FIX protocol is terrible performance-wise, its format requires multiple branching at every field parsing. Even "high-performance" libraries like mFAST are slow: I recently helped a client to optimize parsing for several messages and got 8x speed improvement over mFAST (which is a big deal in HFT space).