I like the concept. I think people are a bit to fascinated on the size of the band. My daughter hates wearing wrist bands, so we put it on/in the backpack, pocket, on a belt loop, etc. The fact you can now switch to other things I think is great. The one thing I don't like is that it is going to be difficult to switch out. With that said, I also understand that the easier you make it to switch out, the higher the likelihood that it can easily fall out, so I'm fine with the trade off.
I may have missed this, but is there a chance this makes them reusable at some point? For example, when you get a magic band, it has your name in it/touches your skin etc. which makes it much more difficult to reuse. I know the thing some people have mentioned is that you will still have trouble switch out due to matching colors. Could a future option be something where they can switch out your puck for a different colored puck? So for example, if you had a blue puck and wanted a green band, you trade in the blue puck which is wiped clean and then are given a new green puck?