I have a SX350 custom box mod, paid $225 for it and (to me) worth every penny. As a RTA user, step down is huge. HUGE!! Someone in this thread mentioned when we realize the crap we are using is really crap, I couldn't agree more. The difference between the SX350 and my DNA 30 is like fuel injection to carburetion. Imagine getting the actual voltage you want.
That is a game changer for anyone that uses a Kayfun-style device, Nautilus/Kanger clearo, any RTA and many genny builds. RDA's not so much because you are going to be hitting above 4.2 volts anyways. I don't cloud chase and I go over 4.2 with a single coil on my Magma. So if you want to join the "Watt War", go ahead. But in a RTA, you will seldom have reasonable need for over 25 watts (even with an Orchid or Fogger). Mods with step down should have another term because they are a different class of beast.
I want a DNA 40, I want a second mod with step down. I wouldn't trade my SX350 though. Temperature control may be ok but you need nickel wire and now we have another issue whether nickel wire is safe to vape.