They really don't multiply very fast. I raise them for composting but by the time I'd have enough to raise to feed to the chickens, I'd have already raised billions of mealworms. So I raise both lol. Look at the Mealworm Farming thread, they are so silly easy to raise!
I use red wigglers for composting. I love it. They can finish off less fresh scraps while the chickens get the fresher kitchen scraps. I use mealworms for treats for my chicks too. I was told I didn't have to cut the mealworms heads off and they love those worms more than anything! I got the mealworms from Grubco.com
I'm raising mealworms also for their treats and I use blackfly soldier larvae for composting and lots of additional treats. They eat bout 1/2 cup a day of larvae. Still waiting for my mealworms (now beetles) to lay and make babies.