The brush-on peel-off substance is probably a PVAc emulsion, and I would be reluctant to use it on a 78.
Qoute fro the Old Colony site:
"The user needs isopropyl alcohol, distilled water and glycerin to make up the needed treatments."
I recall using a product sold by Pickering that was a peel off mask for LPs.
It sure smelled like it contained alcohol - I would not use any alcohol based product on a shellac 78, pretty much guaranteed to destroy it.