Full disclosure: my wife owns an independant insurance shop, but she autocrosses and helped drop the fuel tank on the Suburban to replace the fuel pump, so that makes her one of us.
As to the privacy aspect, that's a subject of personal feeling. All I'll say is from the glimpse that I got from my MBA marketing class, unless you pay cash, stay off the grid and shop in Mom and Pop's with no cameras, there's a lot of info that you make available (some personal that leads to your credit score, other that is anonymous but part of shopper habits). I just don't worry about it, but that's just me.
We have Progressive, and recently accepted Snapshot. I read the terms carefully that came with it. It monitors hard braking - defined as bleeding 7 MPH per second. And it will beep when you do it so that you know and can adjust. It says that it measures G loading in some cases - no more definition than that - and determines speed by time and distance. No GPS so it can't tell where you are doing 65 MPH, but it would notice if you went for a 110 MPH spurt. As was mentioned, plug it in for six months and send it back and they adjust the rate.
Think about it, insurance is really just a gamble. The companies are trying to balance rate with risk. Hard acceleration on the street is infrequent and not terribly risky. Even pulling max-G is a short event relative to straight sections, unless you're at Deal's Gap. The riskiest street behavior is hard braking (following too close in heavy traffic), because one of those times you'll miss. So rather than log a load of data, it would make sense for them to check your braking pattern.
On one car where I think that (hmm, let's see, six max brake events times six laps times two drivers = 72 brake events one weekend day every month) - nope, that car doesn't get Snapshot, I'll take my standard rate thank-you-very-much. But on the Suburban, which is only driven 4000 miles per year, and never at the limits, she figures this will cut the premium 30% on that car once we "prove" how little it's driven.
If I were younger and still hooned more often, then it's not the right product. But in the right application, it has its place.
As a data logger, interesting idea but the terms also mention that it's their property, they fine you if you don't return, etc. I've got to believe that the minimal data it collects is encrypted and not useful compared to other OBD readers.