I only got my NN3 a few weeks ago and I am very happy with it because it eliminated the pain of stitching photos with parallax.
The only parts where I would see potential for optimisation are:
1) The lower rotator leans a bit once the camera (K10D) is mounted. This becomes a bit better when tightening the Friction Set Knob but the bubble level is still slightly out.
2) The markings on the lower rotator are about 2 degrees out after rotating the lower arm from 0 to 90 (15 deg detent ring). I haven't tried other detent rings yet, hence I don't know if it's the ring or the markings on the rotator.
3) Detents allow about ¬±1 to ¬±1.5 degree movement at each stop.
4) A quick release camera mounting plate would be nice as standard.
I don't have another head to compare and none of this stops me from getting much better results than without the NN3.
I would buy certainly buy the unit again and can only recommend it.