Exactly that, it’s just another plugin. Xbuf is a 3D Model Format made by a fellow monkey with the goal to have no import problems anymore. It even supports having a jmonkeyEngine Preview in Blender, since it can do Live-Preview over the network!
The problem with blender is (for example), that when you have a modifier, the jme importer would have to apply that modifier by knowing blenders internal algorithms and also the file structure. This is also the reason why sometimes animations not work (like blender has many interpolation methods jme might not have). Xbuf bypasses this by being a blender plugin which just uses blender itself to convert the data in a jme ready format.
A quickstart guide would be to download GitHub - xbuf/blender_io_xbuf: Delegate rendering to an external render engine (eg provided by game engine) and then set the asset path in the “Renderer Settings” (You have to select Xbuf Renderer instead of Cycles or Blender Renderer). This is important or else the SDK wont be able to locate the textures.
When you have generated an .xbuf, put it into your asset path and you are just one right-click away from having a j3o (so you dont have to load xbufs in your game)