I was skeptical about the app as well, but honestly meeting Spider-Man using it back during the initial test last November one hundred percent sold me on it.
When my time came up on the app I only had to wait for about a minute before I was meeting with Spider-Man (in what turned out to be my all time favourite character experience, though that was mostly unrelated to the queue system). Meanwhile that same day I queued for well over an hour to get a picture with Minnie in her Christmas outfit. The two experiences don't even compare!
I realise that it must suck for people who don't have smartphones, but it really does make for a much better meet and greet experience when you don't have to stand in a massive line beforehand.