I think if I had a tablet, maybe I would be more inclined to use the App, but I just can't read comics on my phone. For one my eyes are like shit, so I have trouble seeing. For two, I want my panels to be large (one of the reasons I like reading digital. On my 21" monitor those pages look awesome).
Now I would use my phone to read comics like Marvel's original Invaders, but only because it has that Frank Robbins art (ewww). I would have trouble seeing the art, so that would be a benefit.