Make the trade if you really want to try sub ohming. Today, before she comes to her senses. Just kidding, each to their own.
The Kanger subtank is a really good tank. There are some things you need to know though.
The good:
A big tank. It's needed as you will go through juices faster at low ohms.
Prebuilt coils. They are available in 1.2 and .5 ohms and they work without you having to do anything but screw them in. It is fairly simple to rebuild the prebuilt coils.
A rebuildable head similar to other chimney type tanks. Simple to build with a single coil. 26g wire, 5 full wraps (ends sticking out in opposite directions) wrapped on a 3/32 drill bit or a 2.5mm rod (as in a coil builder) will give you about a .7ohm coil. works well, and is a good place to start.
Both the prebuilt and the RBA heads have good flavor, and if you want, big clouds. Excellent adjustable airflow for a tank.
The Bad:
You'll need some tools and supplies.
An ohm reader $10, This is a must. It is also convenient stand to build upon.
needle-nosed pliers $5,
flush snipping wire cutters $7,
3/32",7/64",and 1/8"drill bits $2.50 each or a coil builder $15
a set of precision screw drivers $6,
wire in 26g 28g, and most likely 30g if you wish to build high (above 1.2) ohm duel coils (100' rolls for $5 to $10. Less in smaller lengths).
The initial cost can be high to rebuild, but actually it is dirt cheap.
You will have to make a decision on which kind of wicking material you are going to use. This decision is bound to win you friends and make you enemies. Weigh your choices carefully., as you don't want to be caught using cotton balls while vaping with the Ready X Wick aficionados, or using Koga Cotton around the Cotton Baconers. Lord forbid you think about Silica. You'll be banned from vape meets. Its so 2013ish.
The Ugly:
The original Kanger Subtank has a flaw in the RBA head This does not apply if you use only prebuilt heads.
Open up the RBA head (unscrew the chimney from it) and look at the coils. In your case it probably has not been used and is still in the box along with other parts. Look at the blocks with a screw in them for attaching the coils. You will notice that the larger of the two blocks is sitting on a piece of plastic. That plastic insulates the positive post from the rest of the atty so it doesn't short out. If that plastic is a white color. DO NOT USE the rba until you replace the plastic with a grey colored insulator that Kangor will send you free of charge in about two weeks if you send them an email. It is a simple thing to do. You can continue to use the Kangor Subtank as you have been with the prebuilt coils.
The reason for this is that they used an inferior material to make the insulator. The white one will melt in certain eliquids and then short out. Kanger immediately fixed this when they found out. Benefit of the doubt given here.
All in all, I would make the swap. That's just me. If you do swap and then go on to rebuild, I hope you enjoy it as much as I do.