Telemetry isn't an issue. If anything, it can be fully disabled. And yours is done right - all the data sent is properly described and observable. (Although it would be cool if there'd be a helper "let me decide later" mode when I can let browser collect data for a short while, get notified to review it, and then decide whenever it contains anything I consider sensitive or not...)
Maybe this is silly and irrational, but... While it's all your work (and thank you for this!) and decision, it just somehow doesn't feel right that an locally-installed software - no matter how experimental - is ephemeral, almost like it's not a software but a service. With normal AMO addons - even the experimental ones - I can browse the version history and roll back if something's not right. Test Pilot feels like end-user is completely out of control of whatever happens (unless they don't participate and just install from Git repos).