Some of you have already seen my spinning bar, but for those who doesn't here are some pics:
http://homepage.mac.com/kitepics/PhotoAlbum1.html
If you want to see it in action you could download a movie for better undestanding:
http://homepage.mac.com/kitepics/FileSharing2.html
The system consist in two "new" (not so new) features:
One on safety. It has 2 QR inline. The primary (pin&tube) release the bar. The secondary (snapshacke) disconects all in one move, bar and leash from the rider.
The pin&tube is far easier to found and release on an emergency (when you really need it) than a snap shackle (Wichard included). Its symetric nature overrides some of the problems assosiated with rope/ball releases. It does't rotates giving a constant fixed position relative to the rider.
It never jams with sand or moisture, no tangles with the spreader bar hook.
The spinning leash feature of the system is based in a bungie loop attached to the depower by a custom little hook (to get in & out of the loop). This bungie could be trimed for more or less assistance on holding the bar. (I use it as a fixed loop, it extends a little more than the middle of the depower range).
When you unspin the bar after a rotation jump or transition the bungie force the depower rope (front lines) to spin with the bar at the shackle swivel.
As the lever arm is relatively long, the shackle swivel rotates smothly.
It could no be considered an easy home made mod as I have to order some parts outside (metal shop).
Each system has his pros and cons, the kiteproshop bar and the stage 2 are good commercial solutions to the spinning problem but both rely on custom bars. The bungie system could be rigged on any bar with more or less elegance.