Aftermarket copies of this particular cylinder are plentiful, simply because of it's near universal nature, it fits nearly everything British from the 60s and 70s with a hydraulic clutch and also does some smaller cars as a brake master cylinder too.
Since one of it's apps is series Landrovers, I doubt that the modern aftermarket copy supply is going away any time soon. It's probably one of the very few aftermarket bits with more than one manufacturer.
So the issue is one of quality and the quandary is the same as the steering racks, buy a cheap one that doesn't last, or pay more and get something that WILL stay the course.
The problem I have found is there doesn't seem to be any connection between price and quality. Sometimes I have spent more and still got a garbage part. Sometimes the cheaper part is actually better.
Then there are the times when one batch of parts is better made and another is rotten. Or the production of a decent part is suddenly transferred to China and quality goes into the toilet. Finding quality parts for any car, let alone classics, is nightmare nowadays.