Although North Korean Subs are based on Tech Share form Russia I would wadger that this new North Korean SSK would have more in common with the Latest Iranian design then any Soviet SSK.
the North Koreans have to develop there own unique classes and technologies as well as worked with other nations such as Iran to blend in new concepts and Ideas. I would not dismiss them as easy. a Good SSK Crew could be the bane of a SSN, Surface fleet or Sub hunter bird's life. To accomplish This they have the tech gifted them from the Russians in the Romeo class and the PRC, blended in there own ideas, they exported it to Iran Imported it back with Iranian developments and through Bargain, Theft and Bribery have worked to include concept and technologies form Europe the US, Russia, China, Japan and beyond.