They are a poor feeder because they have a high keratin ratio that makes them difficult to digest. Superworms look similar but are more digestible and are just as easy or easier to keep.
I have lost animals because the mealworms damaged the mouths or guts. In one case, a gecko was dead, and a mealworm had chewed through the belly and the skin. Usually the chams, and especially bearded dragons will chew and kill the worms before swallowing them.