I haven't followed r3f development for the last six months or so, but previously I tested a couple of examples that were available as both r3f and pure three.js. I tested them on my old, slow mobile - and there seemed to be a big difference, with r3f much slower. When I brought this up with the devs, they have waved it away saying it's because the demos were running in dev mode (or something similar). However, I haven't seen any genuine comparisons of performance in r3f vs three.js, so for now I'm erring on the side of caution and assuming it's slow. I don't know enough about react to create performance tests myself, unfortunately.