The belt isn't a volley, it requires one attack roll per projectile, and on top of that doesn't call out the lack of allowed precision damage like other volley attacks.
The chimera mask has one decent thing, and a whole bunch of bad. Just shaping it gives you immunity to flanking, which can be pretty useful. However, unless your dm uses a bunch of rogues or other sneak attacking creatures, there's other, more useful, melds to occupy that meld-slot.
And you should never bind two of it's three binds, and the third is better replicated by other melds. Crown meld: you screw yourself over. Get an extra move action and essentially stagger yourself in the next round? What? Soul Meld: omfg when you get access to this, you could afford to have a portable hole full of belts of battle even on npc wealth! Get an extra standard action in return for losing your entire next round. How is that remotely good? How does that make you not screw yourself royally? On top of that, you have to invest a full complement of essentia (not doable until high levels) to not treat everything like it's a secondary attack or worse!
The totem chakra is the only one that doesn't screw you entirely, but the natural attacks it grants would be better with Girallon's Arms, due to power attack multiplicity and essentia improvement, or Manticore belt due to action economy and essentia improvements. Which would also free up the head for more innately better melds.