Here's how to assemble the latest spinning leash:
On a plain bar (without a "re-ride hole" at the end), just tie an o-ring to one end to act as a re-ride hole. Now you can set it up by feeding the leader/line through the o-ring & tying it to a second ring to clip the leash to. Tie the leash to that ring & use a brass clip to attach the other end to your harness hook (where the webbing goes through). It's just as easy to tie that ring to the top of the center adjustment strap, instead of the end of the bar. Set it up the same: feed one leader/line through the ring & tie it onto another ring for the leash to attach to. Now the bar slides up a front line, instead of a rear (which is required with power-steering or reverse-launch bridles). With the bar sliding up either a front or rear line (or even with an old style leash going way up one line) if you use a snap shackle, just add a stopper ball & O-ring (right below the shackle) to attach the bottom of the leash to. That way it will spin freel

Also, check out the Ocean Rodeo "Punch-Out" Bar
This bar releases the trim loop WITHOUT LETTING GO WITH EITHER HAND, let alone fumbling for the release ball.  In case you let go of the bar, it still does have a release ball too. In case you're in the fixed loop, it's got a release on that too. In case you already have a spinning leash with a snap shackle, you can very easily swap that over to this bar also,
or even more easily simply add it to this new bar.