It's not very fast. It worked for some simple animations and a stupid little turn based colony building simulator but I dunno if it could handle something more arcade style.
I wouldn't call the IDE great. It's all on the web and subject to unsurprising latency. I ran into a couple of weird bugs.
But I spent zero time setting up my environment. Zero time building binaries. Zero time on cross platform testing. Publishing (to the jam) was literally pasting the link to the replit on my jam page. Everybody got my source code and a place to hack on it. That is pretty damn cool.
For the curious: https://replit.com/@BrianDavis7/A-Disguised-Far-Muse