I randomly bought a Ful bag 10 years ago at Costco, but still use it today with it working perfectly. I love the 21-in hybrid duffel as it fits perfectly in most over-head compartments. I've actually had flight attendants tell me that it won't fit and then I show them. What's great is the bottom is hard, but the top is very durable duffel, so the ends can fold, plus it has wheels. I usually evaluate an item based on cost versus how long I can use it and have to say, this may be my best travel investment. It is beyond durable and large enough that I've used it for trips upwards of 10 days. It has all of the compartments I need and is very cost-efficient.
