I've now done a little test to check the durability of the paint when it comes to masking and have masked and sprayed one of the fenders. The result is very good with only a tiny amount of bleed in places and a very small bit of paint lifting on the brass rod mudguard stay. All easily fixed with the base colour and fine brush.
I'm surprised the paint is so resilient having thinned it with water. The light green and black are also very nice and again have a slight satin sheen once sprayed on. I think the key here is to let the paint cure for at least 48 hours to ensure it's fully cured and adhered to the primer coat.