I have seen these on a lot of the A cats. A couple of the Italians that charted some boats from me at one of the Coconut Grove Midwinters showed me first.
It does work well to keep the trap from wrapping the side stay if located close, and does keep the handle from spinning around making it easier to grab.
The large carbon tube on the video is a bit of an overkill though. A short piece of polly tubing and a pair of the small parrell balls does the same thing at a fraction of the cost, and getting bonked in the face with a carbon tube on those days where it is not trap weather yet would be a pain.