Boots will not prevent a suspensory strain, but they might help.
For "general" walking, trotting, cantering exercises, I do not feel you need to boot a horse up. The horse moves that way naturally and if they can't support themselves that way, you've got other issues to address.
Now if you are asking the horse to do hard maneuvars such as reining, barrel racing, jumping, etc that is very physically demanding, then boots can provide protection and a little bit of support. (I have looked at the actual studies; it's not as much support as companies claim but they do help a little.)
I personally like the Professionals Choice SMB 3 sport boots on all 4 legs with bell boots on the front. Now, I am not a jumper. I don't know that those boots would be the best for that. Reason I say this, is whenever you see a photo of an Olympic show jumper, they have more of a leather-type splint boot on the front legs -- not a neoprene sport boot.
Just plain keeping your horse in good shape will help the horse from getting injured.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.