What he said....plus its not all about 20 watts for most people. The DNA20 isn't comparable in any way to the China VV/VW devises, the way it applies the power and vapes is second to none in my opinion. Then you get a screen with all the info in one place. some don't like needing more than one button, but I love it and despise navigating and changing options with a single button devise.
It will go sub ohm (not sure about 0.5ohm or less, but I can say 0.6ohm and up) and when it goes sub ohm it will flow unregulated battery voltage with much less voltage drop than a mechanical mod, until the battery voltage has decreased to where it can regulate based on the wattage setting, then regulate until the battery cutoff voltage.
IMHO if mechanical mod users factored in vdrop and etc, they could get approximately the same performance or better with a 0.6ohm coil or higher and setting the DNA at 20 watts, that would give the same vape until the battery was dead.