I am another who loves my BSB. To clear up a few things for you though, the SB is "supposed" to only be a 3.7v device as well. The site does not recommend using anything other than the batteries you can order with the device which are the 18650's at 3.7v. I as well as many others use the SB at 6v with no issues. As for the DB or SBDB (Double Barrel or Silver Bullet Double Barrel) it is a top housing with 2 (yes 2) atomizer holes. You can basically use to atty's or two cartomizers at the same time! That is actually my next investment
The SB is highly recommended but be sure to do your homework as I blew through 4 atomizers in the first 20 minutes of taking it out of the package!
If I were you I'd get on the preorder list as soon as you can. I caught the end of the last one and when they came back for normal business hours, mine hit the mail on a Saturday and was in my hands that same Monday!
Great people over there at altsmoke! Trust me, you won't be disappointed
YouTube - DB SB AKA The Double Barrel Silver Bullet