I used them for a while years ago for my otos and pleco. Honestly, they seemed to like algae tablets better, and I ended up removing most of the pieces I put in there since they barely touched it.
Your mileage may vary, of course. I've had bottom dwellers who wouldn't eat anything but flakes and others of the same species that would clean plants of algae and mostly ignore flakes. It seems to depend on the temperament of your individual(s).
Now, my yellow tang used to mow through the stuff in my saltwater tank. It would trim the sheet all the way up to the clip.