I used one at Radio City in 2003. I was hand-holding a set of ccm4's into my DAT rig, and my D5 was just sitting there unused, so I figured I'd try it out to see what I could get. It was a mono output. Not much low-end. Sounded compressed. Almost like an "AM radio" sound. Output was kind of hot. I was glad I had the recording when I needed to patch ~ 15 sec. in the AUD that I made, but I've never listened to the ALD one again though since it obviously sounded worse than the Schoeps, third row, DFC.
I've worn hearing aids since I was 5, so I didn't feel too bad taking one. I felt even less bad when I learned that they had 10 of them in the box office for people to use. I was taking the first one of the night, and the woman told me I would most likely be the only one.
IMO, these are mostly used by folks who do not already wear hearing aids. The one I used came with one earbud. I do not understand why someone would take out one of their aids to put one of these in at a show. The aid is programed to allow you to hear normally. The ALD is programmed generally for all types of hearing loss. You would have one ear hearing normally, and the other not. Most of the people to do not wear hearing aids that should are elderly. I knew there would not be a lot of old folks at the show I was at, so I really, really, didn't feel bad about taking one.
Again, it was kind of neat, but IMO you'll make recordings that you'll never want to listen to again because they sound so bad, so why bother.