Chicken feet contain the most collagen, so yes, you'll get a super gelatinous broth when you're finished with just feet. It sort of depends on what your ultimate goals are with the broth.
If you are after the collagen/gelatin, you actually don't need to cook it that long. Collagen denatures by 180 or so degrees I think. (This is why the drippings from your turkey/chicken pan are FILLED with gelatinous deliciousness.) I've been experimenting with a ton of different bone broth recipes and methods of cooking over the last few months, and, the gelatin part actually happens pretty quickly. I've noticed hardly a difference in the amount of gelling I get after several hours versus several days.
The additional benefits of actual bone broth come from the minerals in the bones, and that takes a while to get out of them, like 16+ hours. I do think that many of the benefits of bone broth are linked to collagen, but there’s not a huge load of scientific evidence about the properties of bone broth and the benefits. I was a little frustrated after really trying to research it that it seems more fad than anything else.
I personally prefer to use feet within the broth I make with all the other bits. Just feet in the broth is not the same level of flavor that you get with the additional bones, or, especially with meaty bones. I've been doing larger batches right now and using a processor, so my favorite thing is to have them part out the bird, leave the neck on the "frame" and put the frame with neck, wings, and feet into a broth. Incredibly gelatinous from all those joints in the wing, feet and neck, and, plenty of flavor from the meat on the back bones. Otherwise, I keep all the feet, roast the whole bird in a dutch oven or roasting pan, and then throw the feet into the pan and make a broth after we're done with the bird. I leave the drippings in then pan, and just skim out the fat because those drippings have so much collagen in them already.