Sounds like that Tech was trying to drum up business for the Dealership. Most of those aftermarket roof treatments are just "Snake Oil" and not needed. As mentioned, a good scrub once or twice a year and general inspection is all that's required.
Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top