I watched the product demonstrations at the 2004 and 2005 SHOT Shows in Las Vegas, NV and paid LOTS of attention and asked the right questions.
From what I saw, Blue Wonder simply has to be the best and most successful of the instant cold blues. The demonstrated wonderfully deep, even, and consistent coloration, with superb abrasion and rust resistance. There is no characteristic "rotten egg" (selenium smell) or after rust like the Birchwood Casey, Numrich 44-40, etc products.
I wanted some right away. Unfortunately, their distributors seem to be falling down on the job, because it's not that easy to even FIND any for sale!!! I believe it costs something like $20 for a small bottle. Expensive, sure, but if it really works as well as demonstrated in front of many thousands of people, it is worth it! Failing to find a local source, we may have to order some. They have a web site, I believe.