lan61tThere's also the Black Shark cooler , wich i heard is really god , but i don't know if it's compatible
I would recommend for you to get Flydigi Wasp Cooling Fan.
My experience using Active Cooler 3 compare to Flydigi Wasp for ROG3, the flydigi performance is better to cool down the phone. I even use it while charging to keep the heat down.
In my opinion it does the same thing, to cool down the phone.
If there's any hidden features of combining Active Cooler 3 with ROG3, please let me know.