My brother has a Polaris Modular Helmet and he loves it. I found it to be a bit colder than the standard helmet, but it did fit better (the design) and didn't steam up. He did get frost bite on his face while wearing one, however it was extremely cold and it was before we discovered what belaclavas were.
I have had one for a couple seasons - I can't stand it. It fogs up/freezes when its really cold out. And it leaks cold air too... I have a bieffe non-modular helmet that I much prefer, except for the convenience factor of the modular...
Current Sled - 2006 600 HO
Old sleds - 1999 XC500, 2002 Classic 550 (wife's)
I have one and it works great. You have to use the snap in mouth and nose piece which ports your breath out the sides. This will make it fog free. My friend has a BRP one and it is pretty much the same helmet with just different colors and stickers.