Well, I got one free, from my dealer. I really couldn't see anything sus about using it, so plugged it in and set it up on my phone. It gives you some very useful info about each trip you do, including battery charge, fuel level and your parking position. You can also see your route with maximum and average speeds. Once you have recorded a couple of refuels, it will also show your consumption and the trip's fuel cost. There is also a driving style marking system, geared towards economy, which marks high for a gentle touch on the controls.
Which is all well and good. I got used to the app being always on and the trips automatically recorded. Then it just missed a trip altogether. I put it down to a glitch, reset it and carried on, but then the same thing happened again. I was starting to lose patience with it. The final nail in it's coffin came when it hadn't recorded a trip because VW had decided they wanted me to confirm my login details. No message on my phone screen, no red dot on the app icon, nothing until I opened the app to check on the trip that wasn't there! It is now in it's box, waiting for VW to sort it properly.