Are you talking about over fences or as a method of building muscle behind.
If, when jumping, the boots will only enhance whatever hindleg technique your horse already has. If it's not great behind they won't work miracles. If average to ok hind leg technique, then they should work quite well. If you hrse is extravagant behind, then no need to use them.
I use them in the ring on one mare that is good behind but sometimes a little too quick to get her legs to the floor, especially over verticals, the boots just tend to slow her reactions a little and therefore work with her. I have tried them on others, and they have little or no effect.
TBH I'm completely ignorant about their use. I assumed it was as an aid to 'pick up' more in front, the same effect as when I first put boots on my youngster.
I sparked a huge debate about this in December last year regarding the use of a curb chain tied loosely with bailing twine around my horses fetlock which had been recommended by my chiropractor. I was even accused of being cruel to my horse! Since then the poster who protested so angrily against my idea and myself have resolved our differences. The idea of a chain is as follows: A process used in physiotherapy (both human and equine) where a light object is loosely tied around a joint is used to employ proprioception. Proprioception is what all living matter are born with and put simply is 'the knowledge of the relative position of neighbouring parts of the body'. It enables you to walk, stand, sit, crawl, run, walk in the dark, etc, etc. If you have a bad foot or leg you will take weight off that leg and put more weight on the other thus overworking the muscles and bones on the opposite leg. The same goes for a horse. If you put a chain around the fetlock of the bad leg, or a piece of rope, or baling twine or even a string of polo mints (it doesn't matter what the item is it does not have to weigh anything but the horse must be concious that it is there by feeling it somehow) then the horse will automatically start to use the muscles of the leg more by lifting the limb appropriately, which will improve muscle tone and help to aid recovery to that limb. This will prevent the limb from becoming asymetrical. Obviously this needs to be done in coordination with a physio and/or under veterinary supervision."