Took me ages to make a decision on this backpack. Unboxed today & cat has spent most of the day sleeping in it with the expandable space (tent) out. Took it for car ride (had it upright strapped in but it could be laid flat). Handle on top is good for carrying eg putting in car. Took it for walk - I was comfortable, weight distribution was good. Cat was comfortable, didn't jostle much. Mesh on sides gives good visibility & airflow (unlike bubbles ones which can get hot). Front has mesh also but a flap that closes over. Cat was content staying in it on walk - I put it down, opened the flap for her to explore & she just stayed in it. I think the mesh gives cat some security. Then it rained. Rain didn't get in the sides and the front flap stopped it from going in. Cat was fine. At home, she stayed in, then later used it as a cave for play time. When expandable tent is out, if there isn't weight in front it could fall over but this wasn't a problem.
My cat is a devon rex - 1 yr - 4 kgs. There is plenty of room in this backpack for this size cat.