dust in the engine bay and wheels is to be expected i suppose but it is just polish dust which will wash off easily enough.
I have an old bottle of Farcela G10 which is slightly stronger than T-Cut... the Facela compounds get stronger the lowe the number so a polish with G1 would be pretty extreme.
Personally, i'd ask him if its really necessary to go that abbrasive with the polishing, unless the finish on the paint needs that sort of treatment ?