I have noticed that I sell about 1 NXT booster Spray to every 20 NXT's I sell. I also notice that every place that sells NXT only has the NXT wax but not the spray. Many complain about the durability of NXT, is this durability increased when using the spray? Has anyone used NXT then tried layering the booster spray instead of layering the NXT wax? I personally have run out of panels on my 3 cars for any more testing! LOL!