Air is the way to go now. Lighter and less complicated. Running retract servos off the main airborne pack runs the risk of a stalled servo running the pack flat in flight. OK you can have a subsiduary pack but more weight and light modles fly better.

Air up spring down is failsafe. Use these quick connectors and incorporate a restrictor in the airline so they do not bang up and down.

These are Robart and they work well.