Bests & Worsts Reviews from Amazon

I am going to undercoat a couple of vehicles and would like to dampen some road noise also so I ordered a can of QK and some 3M professional undercoating. I wiped the sheets down with acetone. To test the difference I sprayed 8"x8" 18 gauge sheet metal, one with 2 coats of QK the other with 2 coats of 3M. (I sprayed another sheet with Rustoleum truck bed coating, big thumbs down.) The 3m sprayed more uniform, the QK came out really fast. Sound Dampening: I drilled a hole in the corner of each and hung them on a string. I then tapped them with a hammer. This test was fairly close but the 3M seemed to have a lower (duller) thud. I had my wife and son listen, they both chose 3M, They thought I was a goof. Toughness: After they sat for 3 or 4 days sound was still the same. Then I scraped them with the point of a screw driver. With 3M it took several back and forth to get to bare metal and it only came up at the point of the screwdriver. QK came up in one pass and pulled up a wider area to to bare metal. That's all I did. Didn't notice any difference in smell. That's all I know. Ordering more 3M, twice as much or half the price? Update: I jumped to a conclusion on the Rustoleum. Although the Rustoleum truck bed coating goes on thin and runs easily I checked the sheet a couple days later and it produced a hard smooth coat, so I sprayed a second coat on it. After a couple days I tested it. Very little sound dampening but the coat has harder than the the other two and relatively smooth, and as tough if not tougher than the 3M when scratched with a screw driver,