The Kubota branded paint is a much higher quality acrylic enamel and is really worth the extra $$ compared to the tractor store paints that are often much cheaper quality alkyd enamels. The acrylic enamel sprays and covers better, dries faster, weathers much better and doesn't "chalk". Kubota paint is cheap at $10 a spray can and the other stuff is expensive at $6 a can. Price is relative.
Generally. factory paint is a much better deal since they want to encourage upkeep the the higher image and resale values that follow. I paint a lot of stuff and, while I occasionally weaken for small parts such as bolts, an odd color or whatever, it seems I almost always regret the overpriced tractor store paint.