Badmigraine,
I have not tried the Flow bindings, however, used have something similar made by Winterstick in Utah about 14 years ago. Worked great in powder but a little sketchy on hardpack.
Been riding hard boots and plate bindings for about 15 years (last 10 years solid). Picked up a set of K2 Sidewinder boots (1 step below Aggressor boots you mentioned) this fall. Tried them once in Gifu area and put them on the shelf until I can get them dialed in - the upper liner is really stiff and they kicked the crap out of my shins and calves. The K2 Clicker bindings were also a bit of a c