So, just to follow-up with this, today was our ADR day, and the first time we've used any system like this (where someone else made the reservations for us).
Overall, I would give the experience a B+.
Pros:
1) Did get almost everything that we wanted, including a few hard ones like Topolino's, Space220 (not sure we will keep that one or not), and CRT (which was DD's number 1 request). A couple of the time slots weren't perfect, but still reasonably close to what we requested.
2) MAIN PRO: I didn't have to get up at 2:45am! I basically did nothing until I got an email from them at about 8:00am Pacific time.
Cons:
1) Didn't get everything we requested. This was to be expected to some extent. Of those, the only thing we were bummed about not getting was BBB, which was already snatched-up in seconds, apparently.
2) Multiple of the ADRs that they booked were booked as 2 split reservations, rather than a single large table (we have 8 people going). Not really a big deal, but we might not be sitting together at times.
3) The process to confirm the ADRs after they have booked them is kind of annoying. They apparently place a "hold" on the ADR - basically the same idea as the hold time on
MDE between when you book the ADR and the screen that you confirm your credit card - and then they are currently requiring you to call them to confirm that you want the ADR and then secure with a credit card.
The MS rep answered the phone in seconds, which was great, but then the process to confirm took FOREVER. I was on the phone for 45 minutes the first time, then I had an obligation to go to, so I then called back and was on the phone for another 20 minutes to follow-up. Both the reps I talked to were excellent - extremely cordial and knowledgeable. But the need to read them your credit card number 12 different times and then waiting for them to catch up was excruciating after a while. The second rep did mention that they are looking at ways to streamline the process.
All in all, I'm happy I went this route, and would probably do it again, even for a fee. As long as the fee was small...