Nitecore EC4 is a compact and good heat transmission flashlight. Perhaps not impressive for some people, but for me, yes it is. Keep a flat lane for more than 950 lumenes for about 2 hours. Not time step down, thermal management… Is very confortable and lightweight, I have not sensations of 2x18650 flashlight in my hand.
The complete review in spanish here: http://luxlinternas.blogspot.com.es/2015/07/nitecore-ec4-2x18650-xm-l2-u2.html
About great heat transmission, I have meassured temperature in Celsius degrees in turbo mode (little fan assisted) on head flashlight and over mid Body surface, you can see the results:
Runtime with 2x18650 3400mA battery;
Some descriptive Pics:
Animated gif with some flashlights with high mode around 1000 lumens:
Beam over white wall, Turbo: