I did make 2 sets of these based upon the photo in the Coulsons book for a male Harris Hawk. This was a captive bred, calm Harris not a Red Tail Goshawk so your mileage may vary.
I used it on the glove and in a mews with a double door during the hunting season.
Over all I liked it for what it is. Convenience factor is great because the leash can stay on the perch. Just clip on the glove clips them undo the perch clips.
It did manage to unhook itself twice on one leg and once on both legs in the season. The lanyard clip was always dangling on the jess and was detached from the ring, not the other way around. I bought the most robust clips I could find and they definitely hurt my fingers when cold, but not as much as the coastlock which I will not use.
I would not use them in a weathering situation even an enclosed one because they can fail. He does like to play with and pick at equiptment so a standard swivel, extender, jesses are what I use in that situation.
If you are not willing to unintentionally free-loft, I may not be for you, but that doesn't not mean that for some falconers in some situations they are not good enough. I will use this system for tame birds, indoor use, secure mews, or maybe in a Giant hood. (I usually put my bird in a Giant Hood with no hood, swivel, or leash, just jesses when heading to the field because I do not want the leash all knotted up and am not worried about the bird flying past me when I open the door. If I am not ready to hunt the door is not opened.)