Ive never used one, I guess if you want to be "natural" you would carry the kid in your arms... because that dosent involve any 'device'. All of mine were in strollers.
I have nothing against most of them, there are two styles though that I often wonder why theyre sold,
I cringe when I see these ones:
1. most of the kids face is buried on cloth
2. parent's back and shoulder, thats way too much pressure there and once you damage your back and shoulder, youre stuffed for life, basically
Someone bought me one of these when I had Sasha, I tried it for shits and giggles, it seriously makes a little baby feel like the weight of a 5yr old.
And these
Not all "baby backpacks" but the high sitting ones, where the child's head is higher than the parents, only because a very tall man came into our store once with his son in one, and the little baby's head smacked against the door frame, the poor kid, it was a real thunk, blood and tears galore. Of course, it was our fault for having a door frame.