E-cigs are pretty poorly engineered. The first one I bought was the 51 duo. You'll notice that all e-cigs have two small holes either in the atomizer (3 piece models) or on the battery fringe that connects to the cartomizer (2 piece models).
Those holes are there to allow air to be drawn through the atomizer. The air coming through the battery is extremely minimal compared to the amount that will come through those holes. On most e cigs, those holes get covered up by something and basically don't function. The 51 Duo doesn't work at all if you tighten the cartridge down really tight, but ease it off a bit and it starts working very well.
Most people think air needs to be drawn through the battery to activate the pressure switch, but that isn't the case. The venturi effect ensures that the pressure switch is activated by the low pressure zone created across the atomizer when air is quickly drawn through.
The Blu cigs e-cig attempted to address that problem. That's why there's little slots cut out of the battery fringe that aren't there on other e-cigs.
But, they're still using the same atomizer... which was tested and designed in e-cigs that DIDN'T have those grooves. Hence, the atomizer does not function ideally because they fixed the problem too well. The holes in the atomizer are too big when you actually open them to the air properly. Another consequence of the venturi effect is that drawing air faster decreases the temperature more.
A second problem is how the atomizer itself seems to work. It requires pressure to draw liquid onto the element. Since the flow is extremely unrestricted, you have to breathe in HARD to create enough pressure for the atomizer to work properly.
So I'll write up a little guide to using them that should improve the results people get:
1) After inserting a fresh cartridge, twist the battery and atomizer clockwise while keeping the cartridge still. Then withdraw the atomizer from the cartridge and clear all foil/plastic from the atomizer and look down into the cart to make sure there's nothing in there. The foil stops the atomizer from working right if it's in there.
2) Always store your ecig in the pack, with the LED facing down. This helps you get the full amount out of the cartridges. I also recommend having both atomizers in the pack (set into a cartridge) so you can rotate through them to get a more consistent smoke and get the maximum liquid from the cartridges. A cartridge with an atomizer in it will fit in the normal cartridge spots in the blu pack.
3) Breathe hard. REALLY hard; you need to breathe in fast enough to where you're creating suction pressure. To reduce how fast you need to breathe in you could try plugging some of those grooves on the battery; either permanently, or just with your fingers while taking a drag. This will reduce how much effort you have to expend to get a good draw.
The blu cig is definitely not a huge vapor producer. However, it seems fine for smoking replacement. The vapor is about as much as a cigarette gives off, and you definitely get the right amount of nicotine. Keep in mind that the only vapor you really see is the propylene glycol; an INACTIVE ingredient. I'm guessing because the blu carts are so small they reduced the amount of PG.