The success percentage is as close to 100% as you can get. You don't need to zip tie the hands, though, once you're hanging they won't help. If this method fails it is because someone hears you and calls for rescue- if you're in a house by yourself this is very unlikely unless someone walks past the house at the wrong time and hear something. If your legs can't kick into anything to make noise, since they will kick some as your body loses oxygen, then no one should hear. What you hang from must be sturdy. I do think that full suspension, done right is the most reliable method- extremely close to 100%.