yeah...they are ok, our Robotics team used em, and i've used them for Lan Party Staff shirts. They dont last as long, but for 10-13 year olds they are fine. If you can get one of those real t-shirt irons they work a lot better, get much hotter then standard irons. Kids cant iron with that though...
if you can get shirts cheap and find a good source for the transfers (i get mine free) then its definetly a fun project.