New, but if you had the TC6 already and then bought one TC6.1 like me, then you have already a balldiff and a geardiff. I bought one geardiff when I just owned the TC6, so now I have the free choice between spool, slipper spool, geardiff and balldiff. Just the one way is missing in my "collection", because it is too expensive for the one or two races it can be used...

Slipper spool and geardiff are my favourites. They work nearly without maintenance and conserve the drive train.