Yeah, we used Django-nonrel and Djangoappengine for a long time, and Djangae is heavily inspired by it. However the advantage that Djangae has is that it works with normal Django - it doesn't require a patched fork like djangoappengine.

As for performance, it depends what you are doing. Obviously the datastore is non-relational so it scales much better with a lot of data, and you don't have to deal with things like migrations or connection limits. But then you can't do complex queries and aggregates etc. the good thing about using Djangae is you can make use of Django's multiple database connections to store your data in whichever form makes sense (datastore or CloudSQL).