The blade is quite a bit shorter than 4" -- I have no idea why you mentioned that length. It is 3.44", which is the maximum blade length in the Benchmade Griptilian series. Doug's knife is not a custom run. It uses the standard Griptilian Black glass-filled Noryl GTX scales, with a custom S30V blade. The blade simply had to fit the pre-existing handle size.

Maximum legal blade size is determined by where you live. In many parts of the US, e.g., Boston, it would be illegal to carry even the mini-RSK. Some people also consider the axis lock knives to be gravity knives, which further complicates the issue. Anyway, I don't think legal issues, which are incredibly variable, had much to do with the knife's design.