It works well and lots of people do it :) You probably noticed that our docs (docs.getexponent.com/versions/v11.0.0/guides/buil…) mention that it's in beta -- perhaps we should clarify that it isn't related to the actual build product but the infrastructure itself. For example, we just pushed an update last week to make the error messages fantastic when a build doesn't work for some reason (invalid credentials, too many certs on Apple developer account, etc). You still need to download the ipa and apk files manually from a link that's shown to you on the command line and run exp build:status to see updates in the build process.
So it's marked beta because the process of building doesn't feel as smooth and streamlined as it will in the future.