In addition to looking at the amount of miles you drive, Mile-wise also tracks your driving habits via the OBDII device installed in your car and then sends the data to Allstate. The amount you pay per mile is not just paid based on mileage, it also looks at your driving habits - quick stops, quick starts/acceleration, speeding, etc. Most people I know that have used such device found the discount negligible, no matter how careful they think they drive. The real downside is if you were to get into an accident, the other driver's insurance/attorneys can subpoena the data and it could end up costing you more if the data showed anything negative relating to your part in the accident. Personally, I like to keep keep private data private.