Mantid are fine as an occassional feeder. They can have sharp front leg spines that could cause injury. They also need to be raised individually, and since you are feeding mantids crickets and other stuff you would normally feed direct to chameleons, its kinda pointless, except in terms of the novelty / interest factor.
For me, mantids are kewl pets. I only feed off ones that dont shed well (and will thus die anyhow) to my chameleons. The chameleons like them, but they prefer other bugs
You can buy plain, cheap chinese mantid ootha from local nursaries or online, even from homedepot.