On the carby heat on final theme, and going back to the owner and operator having a say in the SOPs...
Hot air is unfiltered and if you are the one who has to pay for the next engine (say AU$30 000.00 ish) you may not like the idea of people landing your aeroplane on dusty airsrtips with carby heat hot!
I teach check for ice on downwind as part of the BUMFCH check then leave it alone. I don't mind if people come from elsewhere and keep it hot on finals, so long as it goes cold for landing.