They don't seem to be as optically "perfect" as newer autofocus lenses which is probably why they sell for less. The big names for "modern" lenses can boast higher edge/edge sharpness, CA, etc., all the stuff that people using digital predominantly go for. Someone in a previous post said he even had to calibrate infinity focus so QC might not be up there.
Also...not autofocus, so that's a huge cost savings.
But still good for the price. And probably higher quality as far as film lenses go, the 7artisans lenses seem to compete quite well.
As to the price consider the size of the Chinese market. They probably make a lot of money selling domestically, maybe even more than they do internationally.
I use micro 4/3, so the price of a micro 4/3 lens is similar compared to these, has autofocus, and probably better performance wide open, but I'd still consider one because of the super low maximum aperture for night shooting. But Fuji lenses are super expensive, so maybe a better deal for you.
Also, maybe 7artisans are better than the likes of Meike, which seemed to review as "soft wide open". And only 1.8 aperture mostly for Meike lenses.
Samyang/Rokinon (Korean) seem to review well, they make lenses for Sony E mount. Seem to review well for some of their lenses, and seem to have a niche, but autofocus technology didn't seem to be as good as the name brand counterparts.
I can say for cost savings for Korean lenses, probably due to lower cost of their staff.
These lenses seem well regarded on this forum, where we are mostly coming from film and like manual focus, but on fully digital forums, lenses from the likes of Yongnuo, Meike, etc. are not really taken very seriously.
