I don't think it's a good thing for general use, but would think it would be fine & perhaps beneficial to use as Yann & others have suggested. The product is primarily formaldehyde and is quite destructive to healthy tissue. It does make hooves brittle if used at all regularly, which negates the hardening effect. Hooves need to remain flexible. Especially soles, which don't need hardening, but they need to *grow* thicker & more concave. It is not reccomended to put the stuff on the frogs, and it is often the heels/digital cushion that causes a horse to be sensitive when not conditioned to bare. Hoof walls also tend to break away at ground level because they need to - they are over long, there are breakover issues, etc.
If your horse was OK to begin with but sore after the subsequent trim, then I'd speak to your farrier about it. Horses should be more comfortable or the same immediately after a trim(tho there are occasional exceptions) and it could be farrier error that has caused the problem.