The Yuin OK2s are not that far from being OK1s for better or worse. They feature the exact same and barely functional canalphone adapter system and have the same appearance. The OK2s are not that far behind in terms of sound quality of the OK2s which is a real pro. These little earbuds sound great just being run straight out of a normal DAP. The sound signature is balanced and pleasant to listen to over an extended period of time and has a lot of things going for it.
One of the major downsides to the OK1s is that they are very demanding where the OK2s are almost the exact opposite. They are a bit harder to drive than low impedance IEMs, but far from as tough to drive as the Yuin OK1s or PK1s for that matter. Because they are low impedance you can run them off almost any DAP out there and still get great sound quality. This is ideal if you do not want to invest in a portable headphone amplifier nor carry such a device around when you want to listen to your music.
The convenience factor with these earbuds is really good, as a package you get a lot of performance without having to go to the extremes. And in terms of sound quality they do have the edge being run straight out of a good DAP.
These earphones fail when it comes to use as IEMs, they simply do not fit well enough. This problem is hard to overcome due to some limitations in the design, ie. offset angle between canalphone adapter and earbud plus the size of the earbud.
If you do not care about having a pair of pseudo canalphones and use them as normal earbuds you are in for quite a treat since the sound quality is far ahead of that offered by normal earbuds. They are still pricey, but they do offer a somewhat spectacular sound quality.