It depends on the application.

For a road going car they are fantastic as they still allow you to parellel park normally etc, they just dont effect normal road manners at all, and on tarmac they work very well, on loose surfaces though a plated diff is generally a better option than the quaiffe ATB one (although quaiffe do also do plated diffs as well for some cars)

What is it you are going to be using yours for? (ie what car and what sort of use like trackdays or roadcar or racing or rallying etc?)