Personally, I feel these are highly over rated. When I owned one, I was so nervous when I drank out of it that I never used it. If I spend 100 bucks on a single glass, if I damage it in any way I will truly be crying in my whiskey.
Now the knock offs, I can't sing the praises enough. They are identical. The difference is so minimal it's hardly worth mentioning. Okay, so they are glass, not crystal. Big deal. These are dishwasher safe, 4 for twenty bucks and if I break one, I'll just get another off the shelf.