The problem about the free Cloudflare SSL certificate is that you share it with a lot of other sites, most of then with "strange" purposes...
From a security standpoint, there is little to no risk. Worst case scenario one of the other sites is doing something that results in the cert being revoked... and I imagine CloudFlare has a way to just move you (and everyone else) onto another cert seamlessly.
I actually know of your competitor (fly.io, right?) and am giving it a test for something I'm working on that needs the hostname support after Cloudflare got me legging it when they said their hostname system was for the Enterprise plan.