Think of it this way:
Every road has a speed limit and you know you can get a ticket if you exceed it. Think of all the miles you have driven since you got your license. Now imagine that you have never driven a car with a speedometer. You would never know for sure what 25, 50, 75 MPH "feels like." Would you pay $50 to get a speedometer?
A home breath tester is a pretty cheap mod.