Tumble recovery design doesn't fly well...ejection usually bends metal retainer and engine seperates from rocket.  Once it ripped the metal hook completely off the body tube, even though it was installed as directed with reinforcing gauze and plenty of glue.  Since I was a gas-airplane builder and flier, I was knowlegable in heavy-duty contstruction methods, but it seemed hopeless.  I also tried enlarging the vent hole to reduce ejection pressures.  It has so much glue on it by now it probably flies like a rock. After multiple unsuccessful fixes, rocket is permanently retired.  Besides, with those 1/4-inch thick fins it looks pretty stupid.  This is probably Estes single biggest fart.  At least it was only a buck or so!