While mantids can be exciting for your cham, they are not an economical feeder at all. They eat a ton of insects, grow very slow (take months to be full grown in many cases) and if housed together they will eat each other even if well fed.
I kept them for a while, but it became too much to continually feed them insects and house them separate. I would only recommend them if you are interested in them for fun, but not solely as a food source for your cham.