Should you expect 1.axb5 to win? Youll be disappointed after 1../Kxa1 2.b6/A4 3.b7/a3 4.b8: Q or R/a2 youll only get a draw.
Please note that 1.Nb5+? is falling on 1.../Qxb5+ 2.cxb5/Rxc2+!