There are plenty of setups and eliquids that work really well at lower wattages. The nice thing is you don't really have to care what the actual resistance of the atomizer is that you're putting on it, it will vape pretty much the same. Heck, if you really want, you can put a 5 ohm atomizer on there and it should push out the 8 volts needed to put out 12.7 watts. At that point you'd be putting 1.6 amps through the Darwin and get pretty insane battery life. Pushing 12.7 watts through a 1.5 ohm atomizer would be 2.9 amps, or almost twice as much current.
12.7 is enough to get a satisfying vape off of a dual coil as well, not an INSANE vape, but plenty satisfying. I'd save dual coils for another device if you want to push more power into it, though.
My favorite thing about it is you can save bad setups on rebuildables... If you're trying to wrap a coil for a 3.7v device or a 6v device, and you wrap it too high.. Like "oops I just made a 3 ohm coil, that's not going to work very well at 3.7 volts", you can salvage it by putting it on the Darwin. As you break your setup in and the coil oxidizes and the wick gets nice and broken in, the resistance will change, and what was once a satisfying vape wouldn't be optimal anymore on a fixed voltage, is still a satisfying vape, because the Darwin adjusted to match the new resistance. Sure, you can manually do this with VV, if you notice the resistance changed.
It's also a nice tool to use with the Kick - you can figure out what a good wattage is for a particular atomizer/juice combo on the Darwin, and then set your kick to that, instead of having to readjust the kick, which can be kind of a pain once it's actually in your tube mod.