The deal with Banks is they do a lot of research and make sure their products meet all emissions standards. I really appreciate the work they're doing, and they're one of the largest supports of the diesel aftermarket.
If everyone keeps blowing black smoke and running dirty tunes then we're going to have a real problem. All it takes is one politician to not like it (as in California) and suddenly diesels are outlawed for sale except in commercial settings. Banks is trying to make tuning more friendly to those who are against diesels.
They may not be the cheapest, but they do offer a good product, and they do have the research and know how behind them to really excel at what they do. On a side note, I think BD specializes in exhaust brakes, but the Banks system looks neat because it's more than just a brake.