I would personally steer clear of the Cavallos if you are going to be using the boots a lot. My barefoot trimmer (an endurance rider) told me they don't go the distance and tend to wear out pretty quick. A girl at my paddock has a pair, which she uses on occasion if the ground is really hard or her horse is tender after a trim, but she says she wouldn't get them if she had to ride in them all the time. I don't think the design is very good, and when she rides her horse in the Cavallos I can see them moving around on his foot.
Don't know much about the Old Mac's, ecept for the fact that my trimmer said she prefered the Easyboot range, but each to their own and I can't speak on personal experience. They do look better than the Cavallos though!
I have tried Easyboot Epics, not the ones with the buckle on the front, but an old proto-type that my trimmer loaned to me. They were great once you got the hang of getting them on, was a struggle the first few times, but definately worth it for my horse's comfort.
I really like the design of the Easyboots, where they have the gaiter (sp?) that wraps around the pastern. I have heard that boots like the Old Mac's and such can rub the pastern, but again, can't speak from experience if that is true. Never had a problem with the Epics and I've had my horse in them all day at Pony Club.
I had to give the Epics back, and so bought myself a pair of the new Easyboot Edges. Havent' ridden in them yet, just got them in the post yesterday, but I will let you know how they go after my ride tommorrow.