Subtanks use more power and therefore more juice than the Nautilus for example. You "probably" will get better flavor from the juices but it's not for everyone. Another issue is you "will" need to cut your nicotine level in the juice should you decide to grow into the Sub Ohm world. Most people cut in half or more, 6 mg being the average high for sub ohm users (my opinion).
I have the Nautilus and love it. But I also love my Kanger Subtank Mini's. With a subtank I immediately replaced the wide bore drip tip and use a more restrictive air flow setting so I can continue my "mouth to lung" vape, like on the Nautilus. The Kanger Subtank Mini has 3 options for it's use. It comes with a build deck where you can build your own coils, or either a .5 ohm or a 1.5 ohm factory vertical coil you can just buy and replace like you do with the Nautilus.
There is a large learning curve with building your own coils. You need to understand some about ohms law (sounds daunting but really isn't) so you can safely vape "sub ohm" (which is any coil with the resistance under the 1.0 ohm level). With Sub ohm you'll need wire (usually kanthal but with Temp Control, nickel or other special metal), cotton, and an ohm meter so when you build a coil you can make certain it is correct (not shorted, desired ohm level) and safe before using it. You'll probably want a coil jig to help wrap coils also (Kuro Koiler is my recommendation)
My Nautilus used more juice than my starter tanks, and the Subtanks will use more juice than the Nautilus. It's my judgement that just about everything with Subtanks are more expensive to purchase (unless you build your own coils). I DIY most of my juice so I can save a little money there but even that has a large investment.