Personally, I wouldn't do the Tough-1 synthetic skid boot. I feel like it wouldn't hold up and you'd end up buying another pair shortly.
I definitely don't like the tough-1 economy sport boot. The strap that goes around the fetlock looks bulky in thickness, but actually too narrow in width. I don't like it.
The Tough-1 extreme vented boot may be a possibility. I like the shape and contours of it. Would be interesting to see it in person.
I would definitely NOT go with the old SMB-II technology on the Professionals Choice SMB. I love Prof Choice and all my horses wear their boots .... but not the original SMB-II. I personally like the Professionals Choice SMB-3
design. Much more contoured to the horse's leg and fits much better than the original SMB-II.
Main point --> Don't slack and buy cheap
boots just because they are cheap
. You will get what you pay for. A $70 pair of sport boots will still be cheaper than a $400 vet bill, and a potentially scarring injury. Stick with a good quality name brand. I know we've discussed this over and over on the barrel board with you.