Down jacket I turn as a down pants.

I love this one.
I almost used the same concept to sew down pants from a cheap down jacket once. But with your way, one could wear the jacket for a layer around camp and then turn it into pants for sleeping!

I don't think this conversion would work on me, I'm 6'2". This looks like a good idea if you have relatively "short" legs.

You can just use your jacket on your legs. When it is cold enough, I carry my Costco jacket for use on my legs if the temps drop and I need to supplement my sleep system. Dual use.

Using a jacket on your body and a jacket on your legs isn't multiple use, in my opinion. If it's cold enough for you to be wearing two jackets at once, your legs need insulation too, so you might as well bring down pants. You'd never use the second jacket for anything but legs.

A down vest is multiple use if you wear it on your legs, though. There are times when you'd want a vest and NOT a jacket. You'll use it independently and as part of a sleep system.