No, don't know any way to download a crash report from TestFlight. The only access to TestFlight is through iTunesConnect and all you can see there is a count of crashes per TestFlight tester. iTunesConnect directs you to Xcode to actually see the report. The Xcode view-able report does have B4i module names but I don't see a way to get to the actual B4i line causing the problem. I will add a screen capture of one. Perhaps there is information there I am missing that would help point to the failing line.
Am I the only B4i user using TestFlight and wanting to use the crash report?