Never used one but they might be worth a try if you like the idea of a sling. I never have liked a sling on a bow. If I'm not expecting shot opportunities it is strapped to my pack (compound bow, haven't gone trad yet) otherwise it is in my hand or slung over my shoulder. With a stick bow I could see giving it a try. However, personally my reasons for switching to the struggle stick would be for (besides another challenge) simplifying things, carrying less crap and the traditional feel so I'm not sure a sling would end up on my gear list.
I did, still have it somewhere, didn't care for it, I had a primos sling when I used a compound and loved it. So I tried a bowtote after switched to trad, it didn't seem convenient at all and wasn't comfortable!