My partner and I both tried this thing out at the gym the other day and in one word, suck. I tried it out on a couple different ropes from a very stiff 10.5mm on lead (got more of a workout trying to feed rope than my partner did climbing) to a very supple 10.0mm (almost useable, but still add to bring the ropes parrelel to lower.) Goes Goes from locked off to FEEEEEEEEED! then back very fast. I suspect that it might work on a very skinny rope a little better, but still not great. The only reason it gets 2 biners is the price; which is actually too bad. People might actually buy these thinking that they are saving a buck only to evetually realize that they are going to have to buy a more expensive device later. Save yourself $12 and get a better device the first time.