I have the heavy neoprene ones with the velcro closures, and they do seem to offer substantial support. They also keep her legs nice and warm.
I also recommend splint boots for stuff like jumping, and sports where they are otherwise turning spinning and are likely to get splints or strike themselves. Reining, barrels, etc. Coming from jumping myself, I used to use them on all four legs. I think they are OK for short rides, when they are going to stay clean, or not wear them very long. BUT, I really got burned, or rather, my horse did, by using them on trail. In mud, or when they wear them all day in varied terrain going from wet to dust, they get grime and dirt down inside them that takes the skin off just like sandpaper. When they get wet in creeks, they stretch and slide down. So they aren't worth it. He doesn't strike himself, and upper leg support doesn't seem to be what he needs anyway.
The only reason I wanted to lunge him was to give him a good cardio vascular workout... get his heart rate up, get his breathing up, because I don't want to do fast work under saddle till he's in better shape. If he'd run himself, he can do that without the lunge. Then the other thing he needs is just to get his back back in shape by doing a lot of walking on trail. I'm going to try to ride today.