From May 16-31, it worked pretty well.
We were there (husband and I) the last two weeks of May and used the DAS for his Crohn's- he had his old pass with him so all they did was scan his card, take his picture and then link my band. They asked how many in our party, and when we explained there would be others joining us, they said they had to be physically present to be joined in. Every DAS Pass we had showed up on our
MDE app (android) as a green fast pass experience, and when we clicked on it, it would tell us what it was. Either he or I would have to go up to the fast pass return desk, and wait to get scanned- about half the time there was a scanner that didn't work, usually because of the connection.
Coming back, it would glow blue, then green when we got passed through; if it was less than ten, we were told to scan and then go through. It didn't matter if we had a fast pass for later or not, it always worked, and never took off the later fast pass (we did use it for Seven Dwarves and Toy Story before our FP+ later in the day). If there was an attraction that we had a DAS for that we couldn't get back to, and got a DAS for a different one, they did double check with one of us to make sure we didn't want it, and they also double checked with us to make sure we wanted a DAS pass for an attraction we already had a FP+ to- on the scanners they had in MK and HS they could see our FP+ and what was already used.
We never used more than I think 3 DAS in a day at most just because my husband couldn't do that much- just too much on him. They were very clear that if there were two in our party that needed DAS that they could accommodate it, but that if both were riding that both would have to have times, and those who are on both passes would have to pick one to ride with- we asked because we have a friend talking about joining us later on who has a different condition.
All in all it worked really well; the main issue seemed to be the scanners themselves, which frustrated the cast members- they kept apologizing and saying they had been promised "updated tech" soon... That and the confusion with people in the larger fast pass return lines; when people were bunched up waiting their turn at 7D, TSMM or ToT and I had to swim upstream to talk to a cast member to get a time. No one save for the cast member could hear what I was asking, and often as I was standing there they would turn and then ask since I was just standing.