Its power is to either turn someone to stone, or return a person back into their natural form. This makes it a powerful tool, but only in the hands of a knowledgeable user.
Vasculio stole the Philanderer's Friend from Torrissio and added it to his collection. Sometime later, the Avatar discovered it in Skullcrusher in Ultima VII Part Two. The hero used it to return Fedabiblio to his natural form. Later, the Avatar traded it to Torrissio for the Create Soul Prism spell.