This is the second Sherpa bag I purchased, but the first Ultimate bag.  My Cavalier King Charles Spaniel outgrew my first Classic carrier (medium).  My only complaint with this bag is that the retaining strap used by the seat belt is on the wrong side of the bag.  When placed in the car with the strap to the rear, the air panel faces the back of the rear seat, not the front of the vehicle.  In order to use this successfully in the car, the seat belt now has to strap over the front of the bag, so my dog can have visibility and better air flow.  Sherpa products are great, but this one needs a moment of thought for a simple redesign.