I have a Trekker, and love using it for single track. If I'm going to be near mud, I can always tape a few tearoffs on, and when I'm not around other riders, flipping the visor up cools my head down a lot.

 

Just bought it at a good old fashioned bricks-&-mortar store. The staff are very good about matching on-line prices. I can't imagine buying a helmet without trying it on first...

 

UPDATE:

Now that I am on a DS bike capable of over 180km/h (110mph), I simply couldn't live with that visor grabbing the wind any longer. Even at legal highway speeds, with a headwind, it was becoming fatiguing and dangerous.

I ended up cutting a piece out of the visor to allow better air flow under & through it so now it performs MUCH better at triple digit speeds!