From experience with the very similar M3W belt drive, the only way to make it run quietly is to get the alignment correct. That is not a quick or easy task but it does work when you get it all running in line. Some of these belt coatings are better than others but they only work for a limited amount of time before needing another application.
I will chip in with a hearty agreement here. After going through two stock aluminum sprockets, then the SuperMax, then finally settling for the newer stock steel sprocket I did them all. Tried silicone sprays with the same results. At first spraying the belt and assembly does quiet it down quite a bit but it wears off. The steel sprocket finally made it reasonable and still, I had to tweak the alignment until it was just right. What I have now, at post 55,000 miles is a reasonably good system.The belts are practically indestructible and will last up to 100,000 miles with care on a bike.
I still get noise, but that is usually a symptom of driving it hard at speed. At those points everything is loud. It's a loud, open cockpit car with a very noisy drivetrain that was all filched from the last century. It's supposed to be noisy!
