In order to be safe, it should not be chained up to any of the critical air systems... (Gear or brakes) This kinda demands an entire new set of pneumatics, and driven by a servo... If that's the case, you're likely to gain weight, and certainly complexity with the pneumatic version. The servo option is variable and only pulls significant levels of current when applied, if its not set up to bind when retracted. I haven't noticed any specific Rx voltage drop when I apply the air brake brake. I use an eagle tree data logger that records data in 1/8 second increments...

Personally, I'd stick with the servo. I actuate mine about 1/2 way as I'm coming off the down wind leg, then full once I'm in line with the runway and want to start bleeding off speed more aggressively. Its a functional brake when the nose is level or down, nose up, the drag induced by the delta wing is going to be WAY more than your air brake.

Kelly