In writing minigpsd (which logs both the internal and BT gps) I've done extensive tests but haven't reviewed the latest logs.

AGPS frequently improves it, but there still appears to be a fundamental problem. I will get 8+ large bars but no lock for 5+ minutes. Other times it is 15 seconds. NO PATTERN. I get fast fixes near windows indoors and neverlocks under open sky (and the BT has happily locked and shows where all the satellites are, so they aren't all hiding behind something).

When it gets a fix it tends to stay fixed.

If I turn it on when it is near wifi and/or has been near a wifi connection, apparently AGPS (supld) picks up fresh enough data and that will allow a fast lock a majority of the time. But there are still points where it shouldn't have updated but locks, or should have updated but doesn't.