I have two hoof rasps, both bought new. One is a monster an one is smaller. I have only used them on maple. Walnut is easy to shape with a spoke shave. On maple I have experienced no issues. A hoof rasp is a rouging tool. So instead of bandsawing off the area around the cheek piece I use the big old rasp. I put tape on the end to protect my left and from cuts. I run them in a draw filing motion, mostly. I imagine if you tried pushing it lengthwise across the grain it would make a mess. The smooth file like side defineately does not tear anything.
I'd love to have a drawer full of $130 hand stitched rasps but I can not justify the cost. You can buy hoof rasps reasonably a the feed store. I would not mess with old dull ones.
The Iwasaki reasp do cut fast. I have four. I find them to be grabby. The cutting teeth are very thin making the rasp prone to jam in to the wood if you press too hard. Put tape over the end to prevent cutting your left hand.