The McKees Hydro Blue is pretty easy to use as Ron has stated, spray on and spray off. I've used in one of my cars so far. I have the "new formula" paint coating on it's way to me as I type. Hope to try it out soon.
I haven't really used a lot of coatings on cars, but it seems to be the wave of the future. I've used Nanolex Wash Coat and it was meh.... I didn't get any longevity out of it (but easy to spray on and spray off like the hydro blue). I don't think I'd use it again, as I think there seems to be better products on the market. (Just my experience and preference)
I have a friend who swears by the Esoteric Kamikaze coatings. His finished application looks outstanding. But they are expensive! I might have to splurge and buy some of the kamikaze to try out.