There are three sizes of the
Pooch Pack - it can hold up to 15 lbs - if you can! (lol)
As for comfort - it totally depends on the person and the pup. Some people aren't able to use a carrier on their shoulder, because of injury, etc., so it makes sense for them to use this one. If you dog likes "sitting up" it works well. It unzips almost all the way, so dogs can "step into" the carrier, then lean back and be zipped in.
I hope this helps!