Bump I'm interested to know too!
It could depend on both the sling and the baby. My nephew LOVED being tied into one of those wide swaddles that seems like it's just a long, wide, stretchy scarf and you wrap it around the baby's bottom and over each shoulder in a specific pattern so he is tied in nicely. He would sleep in it, facing out, as his mother vacuumed the house, with his little legs hanging out, as though is was the most comfortable thing in the world. On the other hand, my niece, whose mom bought something more structured (it wasn't like a yards-long scarf but it had padded shoulder straps for her and leg holes for the baby, etc.) -- something about the leg holes cut off her circulation. (Or, so my sister-in-law claims. I never saw.) For a third example, my son loved his Baby Bjorn, and most of the time I wore it with him in front. (By the time he was big enough to turn it around and put him on my back, it was easier to just put him in a stroller instead.) None of the three kinds I'm thinking of forces the kids' legs open wider than they naturally are as a baby, and they are very padded by their diaper.
Guess my advice is to look online and read some of the comparison reviews. Baby Bjorn and Snugli are the bigger names in the more structured baby-wearing packs, and there is a world of literature in the swaddling realm on those long, scarflike things.
Nice. Thank you. I saw a lady at the mall with something similar to the one your sis in law might have had buy I was like oh no cause I could only see the babies legs. I swear I thought the baby couldn't breath or something and it looked like the baby was doing the Chinese splits. It did not make me feel ok. I like the idea of the scarf one. I guess ill just try one out see if my son even likes being held like that. Thank you!