PWM is very helpful depending on the ohm of your coil and watts you prefer. A .5ohm coil on the Mini in DC-DC mode vapes at actual battery level regardless of the setting (depending on battery level). On a fully charged battery you are pushing way more watts than you wanted. I set mine a 5 watts and the vape was the same as 25watts.
Switch to PWM mode and its like night and day when you change the watts.
This probably wont make much difference on a 1.6ohm Nautilus coil. At 1.6ohm and 4.2volts, you are at 11watts. Thats well within its comfort zone. On my 1.7ohm cartos though its a bit hot and hard on my cartos.
IMO you did not waste you money, i love mine. My only complaint is you have to push the - (down) button first to access the menu, which of course lowers the watts by .1. Pushing the + (up) button (first) takes you into the memory preset mode. Its a bit annoying but you get used to it.