Device: Media Center PC 
Manufacturer: IOSPIRIT 
Model: Remote Buddy Universal

It works perfectly for me. There is still quite a lot of setup. Rather than using the list of Plex assignments (shown in prntscr.com/539b6g), I developed a list of my own.

Have you created all the virtual remotes that you need ? You can give each virtual remote a name "AR211". I created 11. Once you've created them, you can use the Mapping pane to assign Harmony keys to each of the 12 available commands. Have a look at my assignments:

http://grapevine.com.au/~brooke01/My_Harmony_Key_Assignments.pdf

The assignments in the "Raw Key" and "Key" columns should be the same for everyone. I set the function performed as shown in the last column using the Mapping function and various custom and built-in actions etc.

Cheers.