I've being running their self-hosted version, and it's kind of OK.
Nowhere near as nice as, say, GitLab's Ubuntu packages which you can simply apt-get install, unattended automatic (security) updates are available and work well, and it's been mostly a set-up-and-forget type of thing. For GitLab, backups and most ops procedures are well documented.
Sentry, on the other hand, requires you to run a script to upgrade with their docker-compose thingies. You must remember to upgrade.
Self-hosted Sentry runs on docker, which on Ubuntu is a bit of a security shitshow what with docker side-stepping UFW and all that.
Recently Sentry tripled (seems like) the number of containers they spin up, and it seems much heavier than a couple of years ago. You can still get away with 8G RAM, so it's not really that bad, to be honest.
Backing up Sentry was simple enough. However, a lot of questions are answered in the style "if you want to know more, buy the enterprise version". But, I've backed up and restored a Sentry system and it worked out OK, so I guess we're fine. Unless they change something, and then we're hosed without realizing it.
So, Sentry's self-hosted version is OK, but clearly not their number one priority. I have no idea what Sentry would look like with a self-hosted distributed/HA setup. Our data protection policies would absolutely prohibit us from using their cloud services, so maybe I'll have find out, but I'm not looking forward to that.