They are very unique and break up the profile of your mask lens as well as stop the glare on sunny days. They can be custom ordered and made to your design.
A few friends as well as myself puchased a pair of them. They are ok for hyper or concept ball, but they distort vision (looks like a screen door). They are totally useless in rec ball, it is difficult to see and a real pain to clean off.
Personally i would spend a few extra bucks and get a mirrored thermal lens, they are much better for tourneys. If your looking for something for rec, invest in goggleflage, they really break up your mask and help to blend.