I tried Fly.io when looking to move away from Heroku. Some really cool stuff, I love their focus on multi-region apps. But it just felt like too many under documented things and edge cases and the support didn't seem like it would be there for me when I really needed. I ended up going with NorthFlank as my Heroku-replacement, they've had the odd hicup (mostly related to me being the first customer on their us east region) but communication and support has always been incredible. Really happy I choose them.