Another thing to consider with these different fender hangars, some of which like the first one in FlyWright's post seem fairly practical, is the rip-off factor.
Unless someone actually wants the fender itself, the chances are that a knot around a stanchion will go totally ignored. But something like the fender hanger in post #1 of this thread could entice its disappearance simply because it looks expensive and "cool."
One reason, but not the main reason, we rejected the idea of using the fender covers we were given was the boat's name embroidered on each cover. Besides being over-the-top pretentious in our view, the name would have made them stand out. As such, they would be that much more susceptible to being "disappeared at."
We don't have much of a theft problem in our marina, which is surprising considering how big it is. But dinghy motors and boathooks and this, that, and the other thing go walkabout on enough of a regular basis for most everyone to take precautions about this kind of casual or opportunistic thievery. So most marina tenants avoid leaving attention-getting stuff on the outsides of their boats.
Putting fancy fender holders like the ones pictured on one's boat might be a bit like putting a shiny piece of tin foil on the lawn with the crows looking on.