We use them all the time Chris - obviously what your fitting has to be in better condition than what you're replacing!
We try to use new parts only in our community machines simply because of the inconvenience to the patient if it should fail sooner than expected.
With the in-centre machines it has never caused a problem and no one has ever lost any dialysis time that could be accredited to a "preloved" part being fitted.
MHRA are obviously not at the sharp end of a budget being obliterated by over priced spare parts. In theory I'd use new parts every time but in the real world it doesn't quite work like that.
Ian Wilde