If you're after wheeled luggage with the knock-about toughness and practicality of a duffel bag, then this a great option, says Dan Bailey. But it's not an off-roader.
Wheels on a 40L bag seems a bit absurd. I've got a 65L Osprey Transporter bag which has always been accepted as cabin luggage with no challenge and it weighs about half as much. I can however understand that wheels might be useful on the larger sizes.