I've used them on other boats. I think last was on a GK24,? I do recall them working well.
They came with the boat.
However, Winchers do seem to be very expensive (£65 ish?) for what they are? Maybe they are priced against the cost and fitting of a new winch, rather than realistic cost of a 4" circle of rubber?
Ive heard others say thet they can be a bit of a wrestle to fit on to a winch?