I'm a long time 99x user and bought a pair of M2040s to try out the new top-end New Balance shoe.  While they are well made, great fitting, very nice looking, and very comfy, I had to return them because they are such a precision fit that the extra 2-3mm of space consumed by my prescription orthotic inserts made my feet fall out of the top of them.

Please consider this review useful only for people with orthotic inserts.  I still felt compelled to give these a 5-star review because they are clearly an exceptionally constructed shoe that will work great for most people.  As for me, I'm sticking with the 99x.