Did you read the dedicated thread on the theme park strategies forum? These are free- in fact they are going to be the way you access everything in the near future... It's your room key, your charge account, your fast pass plus pass... You name it- it does it. Some reported not being able to customize until doing online check in so you may want to try that... But even if you are at the "manage your magic bands" link... It tells you all about them there. If you still can't access- call
DVC ms in the am and they can make sure your park tickets are linked correctly etc... Not sure but this may be part of the problem.
Whether you presign up or not is irrelevant, you will be using one when you arrive.,, only disadvantage is the customized look and of course your FP+ selections