I have a different version on my sled, I am doing some testing for Goodwin Performance, the ones I have are from Thunder Products, Inc. They are about a 2.5 -2.75" square, 1 per side of the air box, mounted on top. They have a top mounted slide gate, instead of caps. This allows closing off for conditions. I have some testing information at home, but the most impressive STALKER test number was picking up 2 mph at the 500 ft mark. This is the only mod on this sled other than being clutched. Sled is a sno-pro version F7.
I don't know the price difference between TPI and D&D, but if interested give Goodwin Perf. a call, 847-872-4001.