I have one now on my wife's Z and my Expedition. After 30 days our initial discount saves us about $90 over 6 months. We received a 8% discount on the Expy and 13% on the Z.
FYI, the parameters that matter are total miles driven, number of hard stops (>7 mph decrease per second) and time of day the car is driven. Driving late at night or very early morning is considered dangerous and can influence your discount. Speed driven is tracked but does not affect your discount! My wife forgot it was installed and took the car up to about 90 on a empty toll road before remembering the snapshot was installed. I checked out the Progressive website afterwards and it showed the maximum speed but further research showed it did not affect the discount calculation.
We have to leave the snapshots installed for a minimum of 75 days. Since my wife rarely drives her car she is only averaging 26.3 miles per week so far and I'm sure that is where most of here discount comes from. As for my truck, it seems I have a penchant for hard stops.
