Depends on who you ask and if you believe them.
Some SKS rifles are more picky than others when it comes to simply fitting the mag period. Once the mag is in place function would be a 80/20 prospect IMO. Some folks claim they work just great, if you surf and search this subject on several boards you'll get a mixed bag of results.
My personal experience was that fitting the mag to my Chicom was no biggie. Function was excellent with 17 rounds or less. Perhaps a little tinkering would have gotten the full 20 rounds to load and feed but I never bothered.
They do look pretty cool when installed and are probably a better choice than some of the aftermarket mags out there.