I have to say, on this one they were right. Years ago we stayed at a friend's house, and they had a water bead. It was a one big water chamber 80s type of water bed, in fact I think it was a left over from the friend's childhood. To be fair, I don't think it was filled all the way, but this part of the problem with a water bed. Maintenance, it needs to be filled and taken care of.
My husband got in the bed, and I started going up and down on waves. At some point I did go to sleep, but then I somehow was wedged between the water bed cushion and the protective guide rails. This could be problematic for children, instead of annoying for me. I then had to re-adjust, waking up my husband. It wasn't a good night sleep.
I know water beds have improved since that time. My mom had one with individual chambers, so there was less wave action. If I tried a recent water bed I might even like it, but again, the maintenance, the water filling. I could seem them being kinder than a mattress for allergy problems, but since I don't have a big allergy problem, I'll just keep my bed.