Just to add to the discussion. I have had a set of winchers on my sheet winches since I bought my boat
and I suspect they had been there for a while.
They worked after a fashion.
Key was making sure the line was snugged up under the rubber ring. Then, as you grind, the pressure keeps the line feeding out. But the old ones needed three wraps underneath and even then they sometimes slipped.
Week ago I bought two new ones. Difference is night and day. They grab the line much more firmly and when I cleat off (jamming the line into the groove in the ring) they really hold tight.
At $55, they're a bargain compared with self-tailers and to me at least seem to work
nearly as well.