It was very interesting researching the different lunchbox needs of users. People eat different types of food, but also different amounts of food. The bento box was designed to be narrow enough so that it could sit upright in your bag, but still hold a good single portion. It is perfect for a single portion of sushi (and the silicon clip which holds the fork, can also be used to hold your own chopsticks).
The bento box is half the width of the original lunchbox design and this allows you to carry it upright in your bag. The volume is perfect for pasta, rice or even sushi. It may look compact, but it actually holds more than your standard airline meal.