Crimson trace make great stuff.
Viridian well I am trying one of those at the moment has not changed my mind that the crimson tarce is the best.
But the Viridian is leaps and bounds better then the cheaper versions and well I dont have to mention that you have to watch out for the air softer stuff I think most of us have learned our lesson about the to good to be true ebay deals.
Just make sure you buy from a good dealer tho I have heard of a few dealers putting cheap airsofter lights lasers and sights in the origanal product boxes.
Not any Canadian dealer's just from the good ole USA.