I haven't seen anyone else post this issue, but after our daughter had broken her wrist bicycling she had to see a pediatric orthopedic. He said the two biggest reasons kids come to see him are falls from monkey bars and trampolines.
He decided that his kids will NEVER go on a trampoline, no matter how many safety procedures are put in place. He said the risk of bad injuries is just too high, especially for small, growing bodies. He said the worst case scenarios are being bounced off onto their heads or knocking heads with another kid.
I take this to heart. I think we all want to balance the risks of anything with the benefits. Based on his advice, we do not allow our kids on backyard trampolines. I will allow our kids on the ones in gymnastics centers because I feel they are more strict than some parents...surrounded by foam, one - max two kids at a time on a large trampoline, etc.
I think either trampolines or bounce houses can cause serious injuries. I'd use bounce houses for younger kids and trampolines for older kids who can control their bodies better and hopefully be more safety conscious.
I don't know if that helps you, I just thought I'd add a different opinion.