Most of the time Giant mealworms are treated with a chemical that makes them stay in the larva stage. I do not recommend feeding them to any animal. They are, from my exp used for fishing.
I have fed giant mealies to my geckos and I've never had any problems with them. Granted, I don't feed them souly on giant mealies, but I haven't heard of anyone having any sort of problems with their geckos that are fed giant mealies.
Infact, if you feed your regular mealworms well enough they do get quit big.
I dont think all giant mealworms are treated with chemicals.
I was looking for online stores to buy worms and ran into this one and they have giant mealworms grubco they are callled Mighty Mealys on there. Has anyone bought from them?