No, they are beneficial alright, much so also. You get better fuel economy and better tirewear. your buggy accelerats harder out of the corner. You do need to change your setup a bit to get the moast out of it, like you maybe need to take away some initial steerieng and dial in a little more out of the corner, but when you figure theese things out you will have a very fast car.

As for not using it in the rear, i now Tortorichi used theese diffs all around and got two euro champ titles with it...