i have no frame of reference to plastic armor. i only feel it gets hot due to all the leather, and layers that there are. I've stood in 110+ heat and its pretty much the same as 80 degree heat. mobility shouldn't be effected at all. metal or plastic the plates would be the same size.
here's your answer from Shado:
metal doesn't affect me, the belt makes it so i cant bend at the waist as well. the vest makes me hot, but its not the metal, the everything else, the boots, multiple layers, but i dont get really really tired.
does that answer your questions?