I used 1Password for years. Last year I decided to try out Apple's built-in manager (for which this new app is a pretty frontend for a feature that already existed). I was able to export all my passwords out of 1P and import them into 1P. Then my company gave us all free personal 1P accounts, and I decided to migrate back. I exported all my data out of Apple's password manager and imported it 1Password, then ran a script to de-dupe entries.

There's not much else to add: it just worked. I wish all "lock in" were that open.