This actually isn't cruel, considering you care for the roach properly when it's not being worn. The crystals' weight aren't anything to the roach, since they are very strong animals (due to their muscles being surrounded by bone, meaning more attachment areas for muscles, allowing for a stronger build). The glue doesn't harm them at all, and it doesn't hinder their breathing, since the crystals are attached to the carapace of their thorax, and they breathe from the sides of their abdomens. Roaches molt throughout their lives, so if the roach isn't too old, then they just shed their exoskeleton, crystals and all, come their next molt, no harm done. It's the same as gluing them to a turtle's shell, which would do no harm, what so ever.
When I get my colony of hissers, I'm going to give this a try, one because I love roaches, and two, to see if there is any difference in health or survival of the roaches.
Hope this helps!