Atomizers are for dripping. An example is the HH357 from avid vaper. You drip more
juice in (a few drops) as needed. It can be a very flavorful and warm vape. Not a necessary peice of equipment unless you want it.
The protank is a Bottom Coil Clearomizer. The
juice gets heated on the bottom of the device as opposed to the vivi nova that wicks the juice to the coil at the top. The protank will give a cooler vape (cuz the heat is further away from you mouth) and an airy draw. IT can wick better too. IF you want to use clearomizers, it's worth a try.
Don't get caught up in the "better vape" hype. A vivi on a spinner is fine. I used that exact setup golfing this weekend and enjoyed every vape.