I will start with the 901 review. It's a gettho super-champ. With the USB pass it has the ability to kick some major ... but that just kills it's portability unless you have a porta-USB battery pack. Even then you would be rocking a wire to your mouth. The standard batteries are utter POS (at least all of mine were) that aren't worth the small space they occupy. Battery operated it can barely puff out a few decent hits without going into limp mode which gives you nothing satisfying. It also doesn't need an auto switch, timers, or any other complication. That kind of stuff doesn't belong on the cheapo that already has issues. If I can compare, it is the equivalent of adding power seats and windows to a Geo Metro made of plastic. It's bound to break and it just doesn't make sense. Unless you're strapped for cash or don't have modding abilities, I say just forget the 901.
The KB in many ways reminds me of the same 2nd gen. e-cig refinement that can be expected from the 4 series.
It's a whole different beast though. Hard to explain but here are a few examples;
1. On the KB the carts literally last all day with hard vaping. If you pull the fluff out the cart you will see exactly why. Basically you can vape all day and not worry about dripping, changing cartridges every hour. KB is a very straight forward, basic, vape-when-you-want unit.
2. The smoke on KB is definitely smoother than from 4 series but not as thick. For some reason the vapes from the 4 just has a lingering thick-azz cloud. This seems to be totally unique quality of the 4s.
3. Feel: The carts on the 4s are ciggy sized, the draw strength is pretty similar. It's truly made to mimic and replace a cig directly. On the KB, you have a mouthpiece that's nothing like a cig. For the most part it's pretty heavy so you hold it with one hand while drawing (which is not a bad thing because you'd rock the manual switch anyway)
Some of the similarities is;
1. You can hit them both so hard you can almost taste the rainbow.
2. It has it's own strong flavor... I don't know what it is but they both have a certain taste that reminds me of ciggs. It tastes different from cigs but equally good to have in your constant aftertaste.
3. Both the 4s and KB are workhorses until the batteries are completely out. Batteries life is GOOD, and quick to charge.
4. Sentimental value. Both of them are satisfying to hold, vape, and cherish til atomizer or battery sickness do you apart. If it craps out you do feel like its not going to be the same.
5. Bada$$ factor. BA for short. Your friends may think you are going to start jogging and go pick flowers while you e-smoke. You know you can't turn back to analogs now.
In the end I picked KB for one reason. It's RIDICULOUSLY CHEAP. It's $96 from Janty and that comes with 3mo guarantee on batts, 6mo on switches and atomizers. $17 for extra batt (which comes with 3mo guarantee) so a total of $113 for 6mo of hassle-free vaping action. That's $18/month for the unit, cheaper if it lasts beyond 6mo. That's A LOT coming from an a$$hole vapor-nazi like me.
The 4 series could easily cost a lot more (hundreds/mo) if you had to continuously replace parts (which my EVO blew an atomizer in 2-3 weeks) so it ends up costing quite a lot more than Analogs.
However with all that said if the 4 series had an on/off switch, no control circuits, ditched that tip LED, and came with a 6mo guarantee I wouldn't get the KB. I'd love to try the Dura-C. If it's anything like the 4 series with the above mentioned qualities, I know it's something very, very,
special
.
Hope that helps? I'm no master reviewer or anything but I know a deal when I see one. And I am a die-hard purist when it comes to my nicotine. I want no BS and I want it cheap.
MuZG