We bought the newer + bands, whatever they're called now. It did function to open the doors. For a 5 nt cruise, we didn't bother charging it and the doors still opened. We have about 20 old-style bands from past resort visits that just collect dust now.
I think it was part of the plan. If you don't want to feel like Flavor Flav with a big thing around your neck, you'll buy the new bands.