I bet it is a FSP sourced PSU like the Silverstone ST45SF (80Plus Bronze) or the BeQuiet! 450W bronze one ;)
edit: it definetly is the same FSP housing ;)
edit2: 2015 seems to be the year SFX PSUs finally take off, with Silverstone, BeQuiet, Corsair, Fractal, Dirac, and many more in the ship.
BeQuiet DarkRock Top Flow
it might just perfectly fit on the Asus Impact Z87 in the M1.
... or maybe not ?!
edit: it might interfere with the top panel, though there is some space between the border of the motherboard and the top panel.
also the cooler might fit turned 180ºC
aiming for silence and then adding a AIO water cooler + pressure optimized fans...?
AIO pumps will always make some noise.
NF-F12s aren't really that silent.