I use a Tamiyz TZ (Also have the V 20 spec4 10x2T) and the Motor Cuts out without a heatsink, Put the Heat sink on and the Air Gets around the cooling Vanes and Keeps it cooler by 7 degrees..
So it does do its Job...It isnt there for bling it actually does it s job which is to provide a Bigger Metal surface for the Heat to transfer to giving the motor a better heat dissapation rate..

Heat sinks to count.. They work on Boats, Planes and Helicopters even your PC has a Heat sink so it does work..