Disappointed with the function of the design yesterday due to friction issues I’ve modified it- it now has only one spring and 4 screws. The spring keeps the indexing screw in contact with the v-groove in the mirror cell top plate. Adjustment is achieved by slackening all the screws then adjusting the tilt to focuser angle with the indexing screw, and the focuser-axial rotation with the 2 side screws then all 4 can be nipped up to lock it which is better than just relying on the springs I think.
The movement in the video is extreme but shows the arc of the movement around the ball joint and the function of the swash plate. In real life I’m not sure the small adjustments required justify the swash plate really but it at least stops the screws digging into the aluminium.