I like the concept of the Magic Band but it is overkill. I think they could easily get away with a paper wrist band with a RF chip in it as your ticket. It would be super cheap for Disney to do instead of making guests pay for a super expensive rubber wrist band. Everyone could benefit from it and you don't need a smart phone that gets wet.
The Great Wolf Lodge uses paper wrist bands to open your hotel room and pay for things. It's great not having to worry about your wallet / room key disappearing while you are in the waterpark.