It shoots with primary fire - so of course it costs ammo?
Now, let's talk about its balance. This can be done very easily by comparing it with the HZ12:
Blast Brawlers
Magsize: 4
Damage: 195 x 2 (+ 50 x2 if meleeing with it)
Spare ammo: 40
Total damage potential: 17160 (21560 if hitting with the melee on every shot)
Firerate: 61 RPM
Weight: 9
Cost: 1600
Can parry, has little spread, can melee with aim-button
HZ12
Magsize: 16
Damage: 200
Spare amo: 80
Total damage potential: 19200
Firerate: ~140 RPM (2 shots = 0,2 sec + 0,66 sec pump time = 0,86 sec per 2 shots = ~140 RPM)
Weight: 5
Cost: 750
So, for almost doubling both the price and the weight, and more than halfing your DPS as well as your number of shots per mag... you get to parry and a bit better accuracy?
HRG Blast Brawlers are a hunk of junk!
They need higher damage (and/or higher firerate), less cost, less weight and a bit more ammo (well, it's slightly unfair in the ammo-efficiency comparison, as the HZ12 is kinda OP in that regard).
EDIT:
And I mean, it's competing with AA12 and Doomstick, price and weight wise!
* AA12 is very flexible and good at targetswitching and DPS.
* Doomstick is extremely strong in burstdamage (but outright terrible, the worst of all Support-weapons by a mile, in ammoeconomy and ammo-per-weight).
* Blast Brawlers is neither flexible, DPSy or bursty. It just has the parry and heavy melee to offer, on a non-melee oriented perk. Yikes!