I must admit I used to be someone who thought paint was paint but there is a big difference when you use a quality paint. They aren't cheap but I've found Johnstones paint to be very good apart from their metal paint which isn't a patch on Rustoleum Combi Colour
That zinsser stuff is amazing, all the other manufacturers are taking the nasty stuff that makes paint great out but they seem to be putting it back in, don't want to breathe it in for too long.