There has been a good deal of development since the "Stable" release, and you may even find you have better more stable performance for your newer device, using one of the
"Nightly Builds". The naming of a "Stable" release is something to have a reference point in the program development. A point where all the major components are functioning as expected and you can return to, if a new/different programming approach you try is not working or playing well with the rest of the programming. That there is a "Stable" release does not mean that the other "Nightly" releases are "Unstable". Koreader has matured to a point where you only see problems/issues when new devices are added. When a new feature is added, that particular feature may need adjustments or face unexpected conflicts, but the rest of the program remain fully functional.
It is easy to try the different releases. You just copy over/merge the koreader folder from the download zip, to where the existing koreader folder is on your device.
Luck;
Ken