That's an interesting tool.
But I think there is a better way to tie extended bodies.
Go to the women's sewing store. Wear sunglasses and look over your shoulder
a lot--and make sure no one notices you when you rummage through the panty hose (makes great wing cases).
Then go to the needle rack. Get a few packages of #10 and #13 ultra-thin beading needles.
Put a needle horizontally in the vise. Tie the extended body on the needle. Whip finish.
Slide it off the needle. Now you have a modular fly-body part that can be mounted
on a short-shank hook. Those bow-tie deals a far more clumsy and awkward,
because you end up swapping hands for each thread and/or material wrap.