Yep, I've used this too in simple flask programs. Pretty simple, and it's great when you don't really need to do anything beyond simple data storage and retrieval. It's upsert functionality is pretty handy—particularly pre-DB support. Not that any of this couldn't be done by hand, but why when you don't have to?

Any thoughts on the performance?

It's an abstraction layer on top of SQLAlchemy. There might be some performance hits, but none that have made me question whether I should be using it. The convenience of having a more pythonic way to work with data for ETL scripts is worth it, to me.