Don't know but if I see how many Bitmixer-sigs I see, the operator must make a lot of traffic for break-even I guess.
Two thirds of the posts in this thread have Bitmixer-sigs. I have never used a mixer and didn't know the names of any until they started their sig campaign. Now I would instantly think of them if I wanted to use a mixer. I'm certain they are making money out of their sig campaign.