I used something similar through State Farm. However, after the first year of my "free trial," they wanted to start charging me a monthly fee for the device, which would have reduced the savings I was receiving to about $4/month. So, I just sent it back in. I guess a bugger discount was enough for me to give up my privacy temporarily, ha ha, but $4/ month isn't enough.
Now, I'm praying they get it in the mail, otherwise I'll get hit with a $100 charge.
Overall, not sure if I'd do it again. It was a decent discount, but I expected more given that I only drive about 10 miles once every week and a half.