Italian game, Knight Attack. The Response

I was looking at the database and more than once I've noticed a couple of responses to Italian game Knight attack and I was curious about the commonly accepted move Na5 vs a move I've only seen in three games(that all turned out to be a win for black) Nb4

AKA: 

C57: Italian Game: Two Knights Defense, Polerio Defense VS.

C57: Italian Game: Two Knights Defense, Kloss Gambit

5...Nb4 has a poor reputation and has not been played by GMs recently.

Nd4 (Fritz Variation) is much better, I think.

I'd have to look at games wit Nb4, I don't really see the idea behind it?

Can Black still respond to d6 with Qxd6, as in the Fritz? But the Knight on d4 here is crucial for counterplay....

polerio's the mainline, although I don't understand why. Sticking your knight on the rim?

just play the traxler. more fun.