Gravity / Inversion Boots

[mugwump]

Anyone have a personal recommendation for gravity/inversion boots, i.e. the ones where you hang like a bat? I don't need the whole frame, just the boots -- they'll be used with a rock solid pull-up bar. They'll be used primarily for ab/hip flexor work, not pain relief. The ones I've handled are at least partially plastic, which is not necessarily a bad thing, but they're a gift for someone who is rehabbing and I don't want a spinal injury on my conscience. His physical therapist said they'd be a Good Thing but wouldn't give a recommendation.