Running the engine in on petrol is definitely the go but the example given was for dedicated LPG engines and the criteriea and methods may well have changed since I went to school. The bon ami was to allow scuffing of the rings (for want of a better term) to mate and knock the high spots from a fresh bore/hone. We all know running a new engine in on friction modified
oil isn't 'the go' either.
In the defense of bon ami though, it was an exact measured particle size worlwide and often used to de-glaze engines. If you had an old 555 Cummins that was smokey the recommended and widely used procedure was to add 1 teaspoon of bon ami for each cylinder introduced through the air inlet.
As I said though, they were the bad old days and no doubt things have progressed a lot from there.
Bon ami was also brilliant for bringing a real shine to glass, applied wet with newspaper and allowed to dry before buffing off with clean rag.
I probably spent too much time living in the bush though.