I don't get these as they take away the fun and bonding of feeding 3 or 4 small mealies to the gliders. Our gliders will do almost anything for small mealies.
As for big ones, I never cut off the heads, just man up and stop being such a .... YOU CAN DO IT!! Once the glider get a taste of ONE, you wont have to try very hard to get them to eat more. Then just switch to small refrigerated ones.