This is a script to copy vertex normals from one object to an other, based on SlideNormalThief.
The algo is the same but exponentially faster : each point on the target object gets the normal of the closest point in the reference mesh.
The main difference is the way i find closest vertices on the reference mesh.
For 2500 vert:
SNT : 9s
NNT : 1,3s
For 10000 vert:
SNT : 145s
NNT : 9s
Works with poly and mesh. It just adds an edit_normals modifier on the target object.