Hey Raba, I tried doing the same thing, it took me many hours but I fig it out. After I finally got the .fbx file from Unity into blender the model wasn't as pretty, but the bigger issue is the Rig was not there.
IF you can fig out a way to get the rig and the model from unity back into blender please share you knowledge (:
or pm me how
As for that importer from blnderfbx, I haven't tried that. I'll have to fig out how to install into blenders add ons.
I've never installed an add on that didn't already come with blender.