I dont actualy see the use if a 3 movement heat legs.
Heat builds are generaly static, they rely on either high dmg output(reckoning and magma blast, paired with dessolation and charge/hook) or push mech with suprem cannon and rocket side, and a lava scope, or extra grimson rupture, or the heater build dual corupts with savagery, or flames with heron mark, or some odd grinsome rupture flame heron mark.
The 3 movement feet serve better the phis build for closing distance and anihilation, or energy builds that need to breack distance, and use valiant sniper.
The 3 movement heat feet, don’t really have a use atm, since they dont have a valiant sniper equivelant.
But then again, let us have it and i am pretty sure we find them a use.