I have a Ciener, and may have just got one of the "good" ones. When new, it was quite twitchy; would fail at least one round per mag usually, sometimes more. Now it's much better. Jams only with the weird Aguila SSS load; usually due to the .22 short length brass going somewhere it shouldn't, on ejection.
With the other loads I use (Rem subsonic, Stinger, and Federal & Winchester bulk paks), I don't recall the last malfunction I've had.
It's much 'smoother' now, largely due to the parkerizing being worn off a large area of the slide rails, and works pretty much perfectly. Admittedly, it's taken several thousand rounds to reach this point.
And I have heard horror stories about needing to lighten the bolt, re-shape the ramp, re-spring the extractor, etc, to make them work; but no such problems with mine. I may have just gotten lucky with mine, but I like it a lot.