Not driven either, but do own a standard jcw, but what I've see and read they certainly look better, more power and better brakes will be appreciated in the heavier car and it also runs some 10mm lower than the 'S' so better handling.
Looked into a Countryman JCW a few weeks ago, make sure you equire on running costs for consumables. The front brakes cost a lot more than my JCW Clubby ones but unlike the Hatch/Clubby/Coupe, the countryman doesn't get 4pot calipers and has just single pistons.
