google "baggywrinkles"..... maybe a bit of overkill, but they are the best chafe protection for the sails.
ive wondered abot the wheels also, but i dont see how just using one wheel is any better than the spreader boot for protection. it looks like it would create a hard spot for the sail to wear on.
on my Mac I placed a layer of self adhesive sail repair tape over the area that came against the spreader boots (on both sides)... this helps protect the sail, but the chafe still goes on, although no more than it chafes, it will probably be a few years before i need to replace the sail repair tape with a new layer.