I've got to say that I've had mixed results with KF.
On at least two occasions they have replaced a number plate bulb free of charge rather than have the car fail its MOT. On another MOT occasion one of the exhaust mounts (welded) had snapped and they fixed it securely with an exhaust clamp, again free of charge.
Their Oil Service is very good value if they follow all the checks on the list, and I always watch (discreetly) and in every case bar one it was done properly. When I complained about the odd one out I received a £50 voucher.
Having said that, I would definitely NOT have a service at KF nor go there for any large repairs. Their tyres are no bargain, either.
D