Some of the towns around me use these services. I think it's great. There is still the ability to pay locally for those who don't like to use the app, but everyone I've talked to loves being able to pay the meter without running back to the car when your shopping trip or pub visit runs longer than expected.
They even have the ability to find/recommend open spaces while you're trying to park, which is kind of a joke here because it's not super big or busy most of the time, but I can see myself using that in a big metro area!