For jPCT-AE, does jni make sense?
That's a very general question. What exactly do you mean? Sense in which way, related to which components?
For performance, I want to know how many benefits could be from jni.
I wouldn't expect too much. Most of the time is spend in draw calls and the actual rendering as well as in the game's code for anything none-trivial.
But for physic calculation it does very big difference.