Having spent 9 days with a magic band on my wrist a week ago and spending time on buses and in lines talking to other resort guests about it, I can attest that "spotty" is generous. The wifi in the parks was horrible and the 4g wasn't much better. It was clearly a test and the system could not handle the expanded amount of resorts they added this month.. You could access
MDE and change FPs okay from the resort, but when you were in the parks it was near impossible. You were lucky if you could even access MDE to see your reservations. They definitely have some tweaking and fixing to do before they can roll it out for all park guests. I think if you look at the posts, you will see most of the ones reporting how good it worked were Sept. guests. Oct. seems to be a different story. I will say IF you make no attempt to change anything and if your band works, you probably won't have any issues other than maybe not being able to see your reservations on MDE.
In general we liked the magic bands, but we are not FP+ fans. Having the one we make a run for first thing in the morning was nice as was having them for parades and illuminations, but other than that they are more trouble than they are worth. Having to plan your day in advance stinks, especially with the inability to change your plans, which based on our experience I don't see changing because even when the system was working at the resort, what times were available for the headliners for the next day were extremely limited.