I'm quite happy with the Uke Leash, and have one for each of my ukuleles. I play mostly while seated, and my biggest issue was having to support the neck. I spent more concentration and attention on supporting the neck than I did on fingering the chords, and that made it fairly frustrating. The body of the uke sitting on my leg or being lightly held by the right harm works well for me, but the neck was a pain. I notice improvements now, and the dependency on the Uke Leash seems to decrease, but it was definitely the best purchase I made.
Personally, I'd not use something that hooks into the soundhole. I'd worry about the soundhole getting damaged, though I don't know if that is a reasonable concern.