We saw them in the parks today. They look really cool, but we didn't buy them. The CM said they last two years so we didn't feel we would get enough trips out of them.
To be clear, all MagicBands will continue to work basically
forever for park entry, FP+ readers,
charging purchases to the resort room, opening resort room doors, and Disney Dining.
Those are functions of the "near field" RFID chip in the bands.
That chip is powered, passively, when the MB is touched to the tap-style RFID readers.
What
will die in 2-3 years is battery used by the "far field" (or "distance") RFID transmitter.
The functions served by that are much fewer.
Right now, about the only thing that relates to a guest, directly,
is the activation of the on-ride photos and videos that a very few of the attractions offer.