Mag drills wipe clean beceause you can turn the magnet off.
i use some 90degree ones for ROUGH work, they are good if you arn't fussed if your a degree or 2 out. I use them for setting cleats on RSJ's so a degree won't be noticed and better than by eye.Can't find a picture on tinternet but they are 2 pieces of steel sandwiched between a magnet. MAbey the flat bottomed ones will wipe clean easier like mag drills do. I think i paid about £5 a piece for mine
I've got some magnets from a scrap microwave.
I use the standard red 90 degree ones for all sorts of rough work.
H
Not a problem on AC though.