tactic in the philidor's defence

I wonder about that; white's knight on a8 is going to be lost, and then the material advantage evaporates, with white being mostly in the beginning position with undeveloped pieces...  It's not so clear as it may seem at first, I think.

Ι also think that the final position is highly unclear and I don't think I would dare 6.Ng5 and 7.Nxf7 in an OTB game.My experience tells me that such a loss of time can't be good for white and after Na8 is lost, the position is far from easy to evaluate.