As far as I'm aware if you want to use normal maps, you have to use TangentBinormalGenerator every time your game starts up. Depending on the mesh size, that can take quite some time, especially if you have a lot of meshes.
I'm not familiar with how the internals of this part of jme work, but would it be a good idea if you could somehow pregenerate the data produced by TangentBinormalGenerator and save it along the model in a .j3o. That would probably speed up loading times a little.
What are your opinions on this? (You can tell me that due to the internal workings this is a dumb idea )