For really small flies, #6 tippets, fat fingers, bad eyesight, or stiff cold hands this tool looks to be the cat’s pajamas. Just ordered one from Amazon to test it out – $14.95. Will test it out and report back.
NOTE: From the comments this tool is largely restricted to tying clinch knots. So if you’re tying a palomar for your favorite steelhead fly, you won’t need this. But for clinch knots, I think this is gonna be a winner.