I've used vast.ai to do some fine-tuning just a few days ago. It is indeed pretty great, though some servers fail to start up properly, or have some weird performance issues. I also wish they had more templates to try.
Yeah it works pretty well for the price - just need to be comfortable with running code and putting data on random peoples' computers (which I am for certain things). Someone on HN posted a script or snippet of output on mass-testing vast.ai servers for connectivity and configuration, and auto-labeling them using their API. Wish I could find it now... maybe with the search?