We spent about 7 hours at MK yesterday with the bands. The entry process was the hardest part of the day and it wasn't too bad.
We had some trouble getting the Mickey head to recognize our bands and finger scan at the same time but with a small delay we were in. You really need to have your band on your left wrist or just hold it in your left hand when entering the park to have your right hand free for the finger recognition. I'm left handed so had the band on my right wrist initially but ended up just holding it up to the reader with my left for entry. Once we were in and needed bands for fp the readers seemed easier to use and bands could be worn on either wrist.
We continued to use the bands for our allotted fp times while we were there with no problems. (Our plastic APs still worked at the paper fp machines and we didnt have to do anything special to activate them.) Most CMs were excited to see the new bands and try them out with us. Some greeted us by name while some didn't. I can't decide whether that is cool or scary lol. From looking at CM screen the only info they see is your first name (no last name or gender). We joked around with them about the fp system turning into airport body scanners

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We used the band for food purchases as well with no problems. I did not have a situation where I was using a
Dvc or Ap discount to test whether those discounts would be applied automatically but hope to try that out soon.
i had a print out of our times which I carried with us that helped us remember when and where. I could see situations where you either forgot your phone or had a dead phone etc. where trying to use the mobile app/kiosks in the parks would be a pain.
Since we were experimenting we scanned our bands at haunted mansion late last night when there was no line and we weren't causing any delays for anyone else. The reader turned blue and the CMs could tell us that it was blue because we had a fp time from 9:05-10:05 at space mountain. I thought that was interesting.
The entire time we were at MK we never saw anyone else either using bands or wearing bands. We did however run into a family from our home town 1400 miles away who we didn't know was going to be at WDW. Statistically speaking i would have guessed that we would have seen people with bands before people from home. So it appears that this test is a very small test sample of total guests. Hopefully it can be used to work out the kinks before it rolls out to everyone. Fingers crossed.
We are headed out again today for a test at HS. If you have specific questions you want me to ask or experiment with, please let me know and I'll do my best. I'm testing this out for Disney so might as well test for the Dis as well.