I've run my K Sport 6 pots for around 3/4 years now, predominately on track.
I currently run the 304mm kit under my 16" wheels and have no clearance issues at all.
Overall, value for money they're not bad at all.
Parts are easy to order, either from K Sport or from AP Racing. As the K Sports are a "rip off/copy" AP Racing's 6 pot housing, but use a 4 pot brake pad (kind of a mix match of designs - but that's the Chinese for you!)
However to contradict myself, K Sport (or trading as Apex Performance - Bradford) they are totally useless at having parts available, I've rang a few times about spares or replacements and they've either never gotten back to me or not had in stock for around 6 - 12 weeks! (hence my use of AP Racing)
Performance wise, I can't really fault them, they've taken some mighty stick on track with heavy braking and the heat dissipation is much better than my old Wilwoods.
Only things it would recommend, are branded pads (Ferodo DS2500, Mintex 1155 or Carbotech XP8's) rather than the crap, K Sport supply (garbage and lethal).
Make sure you add braided brake lines to the rear of the car to "help" balance out the braking bias when adding the 6 pots to the front and good quality brake fluid like ATE Super Blue. This should be a good combination of braking performance and help reduce that spongy peddle feel!
Depending whether your going to track the car or use it on the street, choose brake pads that best suit what you will be doing with it.
Also one other thing, don't bother with their 8 pot kits, there mega bulky compared to the 6 pots and the overall pad surface on the 8 pots only fractionally bigger than the 6 pots and I personally feel they are not good value for money.