I have that poster as well, and if you look at it closely...or vaguely really, it's pretty obvious, they call it two different things. On the image where he's facing away from the camera (as you have shown above) they call is a blaster thingie, but on the image where he's facing the camera, it's called a flame projecter. I always thought it was weird, because the bottom one should be longer than the first one, like a pilot on the flamethrowers...but it IS sci-fi, so who cares. 2001 is still the most accurate space movie, and you know how thrilling that one is. Anyways, the point was that all sorts of officially licensed material contradict each other, but that particular poster contradicts itself. Also, that one poster (which had the image where I first noticed the ESB sidearm) with the front and back pictures in a less dynamic pose, they name the sidearm as a grenade launcher. Must be some tiny grenades that erupt from that barrel.
So, this brought up questions I've been meaning to ask for quite a while. What is the general consensus about all the gauntlet weapons? Where's the whipcord come from? Which is the flamethrower? Which is the laser he uses to shoot at Luke, etc? The flamethrower, I would think, is the thing this topic is about anyway. Not only did Jango throw flame from that spot, but also it's where the original flame thrower (which was supposed to actually function) was on the pre-pro suit.