Depends what you are looking for. Very different devices. The kanger has a much small form factor going for it, and looks amazing in the stainless steel version, in my opinion. It is also much lighter, and you don't have the hassle of keeping batteries 'paired' together.
A more direct comparison to the Kbox mini is the Evic Mini VTC, which is a very solid device.
I think there have been few early issues with some of the Cuboids, too, but I can't actually recall what they are. It is heavy, and quite square. Not one for a suit pocket. Having said that, the battery life will be much better, thanks to the 2 batteries. (I prefer to keep a couple of spares in another pocket, and keep weight and size down though).
I am looking to go back to VW from mech just now (I used to have a VAMO that went up to 15w, if I recall). I am veering towards the Kbox. But also considering others, such as the Evic Mini, and the Smok R80. These two have the advantage of firmware upgradability (over the Kbox). But the Kbox in the steel is really beautiful in my opinion. If there was an Evic Mini VCT in Stainless Steel, that woul definitely be what I would have.
Personally I have ruled out the Cuboid for now, as I only intend to use one VW/TC mod (at the moment) and smallish form factor and aesthetics are important to me.
You just have to decide what is important to you.