I have a bPay band, it works fine and it's a neat idea with a few flaws at present:
- All your purchases are batched under a single top-up on your bank account, you need to review the bPay account to see what was bought
- The card is quite small (a bit larger than a mini-SIM) but it's inserted into a thick pocket in the wristband and the overall 'bulge' is HUGE and uncomfortable.
- Because it's "one size" the wristband is fastened by pressing a very flimsy plastic clip into holes, this takes AGES and doesn't seem safe at all. It's far too thick to stretch over your hand and I'm sure the clip would break very quickly.
- You can't go out with just the wristband because obviously not everybody accepts contactless, and it can fail.