When an outlet is opened only briefly, TankBoost pump does not activate, is this normal?

Yes. TankBoost is designed to activate the pump only when the control module recognises that static pressure has dropped a set pressure. Drawing only a small amount of water from an outlet is not sufficient to activate the pump, until the value falls below 1.5 Bar on TankBoost 3.0 Bar or 4.0 bar on TankBoost 5.0 Bar with the outlet opened.