Kevin,
Do you know the reason why FTE usage dropped from 200 to about 50 at the end of August and then recovered again?
https://metrics.torproject.org/users.html?graph=userstats-bridge-transport&a...
I had a guess that maybe it had to do with availability of new bridges. If a bunch of bridges got blocked and then new bridges were made available, that could explain it. The 4.0-alpha-2 release was on September 3, but as far as I know it didn't contain new FTE bridges. They could have been added to BridgeDB, I suppose.
David Fifield