I have to admit I didn't use this traveller for hill walking yet, more like around the house.
As a part-time working mother, I try to do the housework as quickly as I could so I can nip out to have a cup of coffee with other mothers ;p
My one years old doesn't like to be left alone and hate being in her playpen! So the only way I could do the housework (too many to name!) and even put washing out on the lines, I just carry her in this backpack. So she is behind me and I can do things.
It is very comfortable to use and I don't usually feel her weight until an hour or two later. This is definitely more comfortable than a sling as the weight is distributed all over your body (mainly shoulders and hip). She also loves being able to watch what I am doing. She does ocassionally pull my hair when she is bored.
I would imagine it is comfortable for her as she fell asleep a few times (I wonder how with me moving about!).
I would recommend this for hillwalker as it is very comfortable.
Just note that this is still quite bulky and I don't like the idea of my baby sleeping while 'sitting' up (she still need her 2 naps a day). So it is not something I would take it away with me on holiday (unless is a hill walking holiday). I still prefer a buggy so she could sleep in it (and carry the nappy bag and shopping too!).