Horses have a natural jump on their own. There’s a point where you can enhance technique. I don’t believe breastplates do that. I feel like some breastplates if fitted incorrectly can cause a ‘block’ In a horses jump and restricts shoulder movement but when fitted properly it’s mainly just an extra piece of tack to assist with the saddle not slipping back :)
I read the study and I don’t trust it. It was done by Fairfax who produced a breastplate which supposedly doesn’t affect a jump but that’s simply a tactic used to convince people to buy their product. It’s a biased statement.
More studies need to be done but not from sellers themselves.
Not to mention, there are multiple types of breastplates.
The training, tack, and individuality of the horse and rider need to be accounted for.