BluHeaven- Nice job, you're sure getting your TT all spruced up! Like you, I don't like Griot's sprayer for use with the Undercarriage Spray. Too easy to spray stuff I don't intend to. There are better sprayers out there, I got my last ones from TOL. I ended up "painting" a lot of the Undercarriage Spray on with foam brushes, only spraying the tough-to-do spots.
Heh heh, I think I just coined a new Autopian acronym: Griot's Undercarriage Spray= GUS
Fr0zen- As I recall, another AMG pilot compared the two products and preferred the Griot's. I barely remember the thread, but I think he preferred the way it "aged" as it started heading towards needing to be redone. It's gonna be a personal preference issue. I've only tried the Griot's, and I DO like it. But beware! It can be one MESSY product! Heavy silicon content, very oily until it dries. Don't get it all over your tires or your driveway or yourself. Don't get it on your good towels either, it doesn't launder out easily. Watch how you interpret those caveats; remember, I DO like the product. In MY experience, the GUS lasts until you wash it off with something sorta strong, like EF-HI. I always end up getting too aggressive with my wheelwell cleanups and have to re-apply it because of that. Otherwise, it'll last a while.
BTW, just had body work done on a car that I recently used the GUS on. They worked around the specific areas where I used the GUS and NO, there were NO fisheyes or other problems. But this shop knows me and knows to REALLY prep with wax/silicon removers when doing my cars.