I'd agree that, for the £100, it's worth every penny; I pre-ordered my
MCS a year ago and waited until production in April.
It can be a challenge but, if you're in a position where the LSD is working hard, then you should be giving it 100% concentration, too. I can imagine that, if it grabs you by suprise on a damp patch, you'll end up with... a damp patch!
I was recently conducted on a closed road with lots of swoops and dips, following a 210 turbo without LSD (mine's a standard R56) who knew it well, and I was suprised that I could stay with him on the straights (but not gain). Diving out of the twisty bits, I almost was ramming him; I could hear his exhaust note clearly and the reason was 1) I was able to use less gears and 2) my ability to put the power on the road. When it's doing the 'bucking bronco' with the steering and sliding around, then you know it's on your side!