The fluted hammer is lighter, with C02 this deceases the time that the valve is open, and also lets the mainspring accelerate the hammer forward a bit quicker (backwards from where the paintball is directed)
So yes, by having a lower mechanical dwell, less air is used per shot.
However, on HPA with a tri fluted hammer I woulds strongly suggest getting a red or heavy mainspring. (to use with medium or silver valve spring)
The reason is because with HPA the pressure goes down (c02 is 850 (ish)) HPA is 800 PSI (usually unless your tank has a higher output)
This decreases the velocity, so you have to turn your Velocity adjuster in to raise it. with a lighter hammer you have to turn it in even further, This results in the velocity nut stopping the hammer from catching the bolt when you pump it. Preventing you from actually being able to shoot.
Using the hard mainspring removes this problem.
This is an issue that I had with my phantom, Tri fluted hammer using HPA.
the red mainspring was my solution.
If your curious. screw in any air source and screw in the velocity nut all the way in. You will notice that even if you pump. the trigger is still slack and nothing actually happens when you pull the trigger. Questions Regarding Springs and Hammer Catching
a read for my thread: its dead. so no need to reply to anything. however the info may be useful to you.