Online primary key migrations is some interesting voodoo. We ran it in production from the v2.x days before they moved to a new versioning schema and the support was really good. The paid support is worth the enterprise license. It's also good to see the added work on supporting ORMs for shops that use it. We used SQLAlchemy heavily and had to do a lot of work to fix our app to work around the transaction retry error…
Retrying transactions is something every app ought to handle, but it's rare enough that most codebases I've seen just punt on it.
The thing is before CRDB the application was operating just fine in MySQL's default isolation level.