Note: this post is long, but bear with me.
I'm intrigued that you chose to block DG, considering that "advanced" traits have never been blocked before. Wouldn't it be equally possible to just force the effect to only work when holding one gun? (This means you have room for a more appropriate block, like TaN or EE, and that DG still won't be chosen on account of it being useless with the master trait.)
Otherwise I like the sound of it, we could use another Juggler after losing it on MFa. Frankly, though, I can't imagine NOT using this build if it were available. You are effectively reducing your firing time by one-third which, compounded with the -60% of SoaG(x3) and -30% of Fin(x2) (we'll say you get the second one later because it'd be foolish not to) and that comes out to (0.667)(0.40)(0.70) = 0.187 firing time. This is comparable to the blaster with the same, non-mastered trait (looking at 5.5 shots per seconds as opposed to the blaster's six), not to mention you can still get SoaB and WK...and it costs half the bullets of a MGK build!
The second benefit is also quite strong, as I assume it immediately stops the clock whenever an enemy moves into your sight range. This gives you roughly six shots before most enemies would be allowed to retaliate, and if we're looking at 2d4+6 (SoaB(x3),SoaG(x3)) = 8-14 = 11 damage per shot, that's...pretty insane. Not to mention you can raise that with some power mods. Also, this could alternatively overlap with Cateye, granting less damage but more time to shoot before they even see you. (This is assuming that there isn't a mechanic already in play that forbids more than one master trait, although I figure it'd be added once there IS overlap. Just a technicality.)
I like it, I really do, but upon first inspection it sounds vastly overpowered. Blocking EE or TaN would help for starters.
I should probably comment on Bullet Dance, too, while I'm at it. My first impression is that you have a permanent overcharged chaingun, with an emphasis on damage instead of shots. Firing all six shots at once (in BOTH pistols, mind you) is (2d4+4)x12 = 108-144= 120 damage (neglecting armor, which is -12 per point) once you hit level seven (probably 2d4+6 by the time you're done, which averages 144). This kind of damage per second is sickeningly overkill. Furthermore, you can just as handily full-auto a single pistol, swap, then full-auto the other. It wouldn't be a bad idea, however, to shoot out half your bullets and full-auto the rest. If you want to make it more practical I would suggest semi-auto (ie, 3 bullets per burst) instead, which will still kill most enemies in a single burst.
To balance properly, doubling the fire time is probably the best way to go. This is basically saying that you are uninterrupted while firing the burst but must be prepared for the retaliation afterward. According to your trait blocks, decreased accuracy would be fixed with a single EE, and shrapnel damage doesn't really make sense. Also (again, as a technicality) you still leave the way for MGK open. I can only imagine using full-auto after dodging an attack, OBVIOUSLY reloading, and starting over again. Get a blaster once this trait's already in effect and the game is already over, I don't care if you're doing Nightmare! Mortuary.
Frankly, non-Kata pistol builds are quite powerful as it is: the problems tend to stem from lack of bullets and exposure. That was my intention for the Sharpshooter build, which effectively blocks SoaB (preventing monster-like damage) for the ability to screen your advances into the next room, and an effective 20% bonus to your overall damage which carries on to other weapons. As with MFa, it's a specialized build that has potential for other weapons, thus making the way for more usage outside of its respective challenge. I like the others, but I believe they focus on that which has already been addressed in the other traits.