Well, the most annoying design flaw is the totally inappropriate DC-IN connector: http://forum.banana-pi.org/t/bpi-m3-with-r58-h8-a83t-chip-on-board-so-cool/886/6?u=tkaiser
At least they changed that on the most recent production batch. So people who buy this board now or in a few months aren't affected by problem N° 1. But unfortunately most people don't understand the relationship between consumption, cable/connector resistance, voltage drops and (improved) heat dissipation. With an original BPi M3 using the crappy Micro USB DC-IN connector applying a heatsink or even heatsink+fan is absolutely counterproductive since this will decrease stability even further since undervoltage/undercurrent situations happen more often/early.
And unfortunately this board has so many other design flaws combined with non existing support, crappy OS images and no real community that it's really hard to do something useful with it.