Seems like a huge information asymmetry, though. Anyone who's ever dealt with an insurance claim knows that they find any nitpick to get out of payments... having an insurance provider that can say "actually we don't owe you anything because according to our black box, you were 2 mph over the speed limit therefore you were negligent" seems like it defeats the purpose of having insurance.
I like the idea of more accurate pricing based on actual (low) usage, but I don't like that it gives them a disproportionately larger surface area for their lawyers to find technicalities that gets them out of paying claims. When the tollbooth transponders came out, they explicitly said "this will never be used to issue speeding tickets" even though all the data was there... I don't believe MetroMile makes any similar promise.