I will no doubt make use of the medallion when we cruise, but really when paying for drinks it's not much difference to the waiters scanning your cruise card on their iPads, and probably no quicker.
However the main issue I will have with it is the extension they have made for it to be used to undermine the very essence of "Anytime Dining". Princess and most other lines, seem to be selling this up as a major advance in providing us with a slick way to guarantee we dine when we want, where we want. When really all it is doing is enabling them to reduce the number of MDR covers and cut the number of waiters which only benefits the cruise line. I remember back when AD started, when there were more tables and waiters and you could turn up just when you wanted and be seated. Now it seems that most dining rooms have long queues, even if you have booked a time, and even longer waits if you haven't.
To me this is rather like self check out supermarket shopping, where the only winner is the supermarket.