I'm not a fan of slings with padded rails, they don't allow you a full range of adjustment as the rails cant be pulled to far.

They do ok with an older baby in a hip carry, but with a small baby the rails can flop in over baby restricting airflow in a reclined carry and as you cant pull the outer rail tight it can be hard to get a secure tummy to tummy carry. If you look at pictures of a true ring sling (I love Maya Wrap thought there are plenty of others) you can pull the fabric through the rings with no padding in the way so you can get bub nice and snug and well supported by fabric right up to their shoulders in a tummy to tummy carry.