so uh... i had no idea these even existed... what would be the pros and cons of a helical diff over the viscous units that most of you know and love? and i'm assuming it would fit in the stock case but with some kind of different side shafts or some such shenanigans, but what the hell do i know? what problems could be encountered trying to drop one in? and what kind of $$$ am i looking at here?

EDIT: funny what happens when you search FA for anything related to nissans... you usually find your answer... how hard would it be to swap the guts from the s15 diff into an s14 pumpkin?