WOW is the little piano hinge the chute door? I was amazed that it flew open and just stayed there--no fluttering or flopping!
That was one of the tests we wanted to perform last weekend. The doors were mounted at a specific angle to actually "fly" in the open position.
The goal was to get the angle perfect so the door didn't slam open or stick shut. Getting the angle right meant the door would open when released even if the spring on the pilot chute didn't push the door open.
We also couldn't put a tether on the primary door since it would get in the way of the secondary if we needed it. The angle seems pretty good as you stated in your comment, it rides pretty stable in the open position.
We didn't get a video of the secondary chute door in action, it wouldn't have mattered anyway. When we deployed the first chute, it damaged the secondary chute door. It took many views of the video to determine how, but it was actually a pretty simple problem.
If you watch the video of the chute release, right when the tether goes taunt, you can see the door get booger'd up. If you pause it just right, you can see a green sheath being thrown up. It turns out the green sheath is on the reserve chute. When the primary was packed, we accidentally let the secondary tether get on top of the primary. When the chute snapped tight, it threw the secondary tether up and broke the door.
It is an easy fix for both the door and preventing it from happening again. We had made molds of the doors in case the became damaged and have figured out what we need to do to separate the tethers.