Haven't used it, but we were also offered it for free. My husband researched it and we decided to decline the offer. If you have State Farm Insurance, I believe Ting is also owned by them.
I found a reddit post today where one person claims they read the terms of service and it includes this wording: 5. You agree to allow State Farm Mutual Automobile Insurance Company, for the benefit of itself, its subsidiaries, and affiliates, including.... (blah, blah, blah)...access to your Ting sensor data, which will be made available to State Farm during the program. (........) STATE FARM MAY ALSO USE THE DATA FOR PURPOSES OF INSURANCE UNDERWRITING, PRICING, CLAIMS HANDLING, AND OTHER INSURANCE USES.
I personally haven't read the terms of service, so can't verify if what they posted is true.