With the ability to shut this off, I don't see the justification in the extra cost of a worthless gadget. I have not had a ticket in years, and all my over the road truck driving for 10 years I never got a ticket or log violation. I obey the posted speed limit signs as it's not hard to do if your concentrating on driving, which you should be.
I assume this is for those that want to send text and not pay attention to driving, but don't want to get a speeding ticket either. Lawbreakers can shut it of anyway.
My grandma could use something to speed up her car to at least match the speed limit. Now that would be useful.