My understanding is that the assisted listening devices are designed for those who have hearing loss, not total deafness.
People with the type of loss these devices are designed for have difficulty with hearing detail through ambient noise. They may wear hearing aids to help with this problem, for instance hearing table converstation in a noisy restaurant. The SPLs of concerts probably overload most hearing aids, so the ALDs are likely the best solution for these folks for live shows.
ALD devices, based on recordings from them I have heard over the years, seem to deliberately target the midrange and upper frequencies. I expect that with the heavy bass present in a concert, the ALD only needs to fill in the mid-range and higher end detail for the user. Probably works just fine in a concert, but take the feed alone and it's thin, nothing like a IEM feed, that is full range.