I agree with Skepti and just wanted to add one or two things:
Dubia's are excellent at hide & seek, therefore if they're left in your tank for more than a few minutes, they'll squeeze into the smallest and darkest of spots so your beardie wont even know they're there, thus defeating the purpose.
The other thing is if you have a glass tank as an enclosure, they might be able to climb up the silicone sides; especially babies, since they have extremely grippy(?) feet and can climb up surfaces that larger dubia's can't.
I love them as feeders though! They're so perfect