I recently opted to try the Liberty Mutual plug in tracker as they told me it guaranteed 5% discount minimum and up to 30%. The criteria they track is number of miles, fast start, fast stops and time of day. Driving between midnight and 4am is higher risk. I find it odd that they do not track speed. Also I am noting that their use of fast stops and starts does not take much to qualify for an event. I can logon and track all of the events that are registered. Overall not very happy with it as my neighborhood has an entrance that you must accelerate fairly quickly since it is a curvy hill coming from both directions. To go slow out of their presents much more risk. I know these are very general factors and it is voluntary but just sharing my experience. By the way my discounts are showing as 9% for sable, 17% for grand marquis and 11% for Montero. Better than nothing but I think it would be difficult to get over 20%.