Hello!
The problem is not the OS version or the display resolution. Currently our tablet application has the same UI design of the desktop version, and we consider it usable only on displays with a size equal or bigger than 7″, this is why the Note 4 is not compatible.
We’re working on a specific version for smaller screens, you can follow this Feature Request to know when we’ll release it:
Offering a NoMachine client for Android smartphones
https://www.nomachine.com/FR09L02828
If you want to try the application on your smartphone you can still do it by visiting our website and downloading the APK version.