This was exactly my experience with it too. It's moved on a bit since then but when I looked at rocFFT a couple of years ago, the documentation was really poor

This was exactly my experience with it too. It's moved on a bit since then but when I looked at rocFFT a couple of years ago, the documentation was really poor and it was missing features. When I switched from FFTW to cuFFT many years ago (~2015), the transition was very smooth, the documentation was great, and all features were supported. They even put a shim "FFTW" compatible header file in so that you didn't need to rewrite your code to make it work (leaving some performance on the table).