The Brain Bag with Packing Cubes is perfect for U.S domestic travel (planes=Southwest, trains, boats and cars). I assume it is also the case for travel within continental Europe/Asia, Australia, New Zealand, the UK, Japan, Africa, Canada and South America.
The problem are those pesky watery areas between continents when one has to deal with airlines and their even peskier carry on weight rules.
Now, it is not about weight and balance because the bag is going to be on the plane anyway so it makes no difference if it is within reach or crushed under the weight of enormous wheelies, in cargo.
Most transcontinental airlines have 2 or 3 classes on board their aircrafts, on some airlines, the higher two classes pay more and get to keep 2 carry-ons instead of one.
It seems to be the job of some people to show cargo...hem coach passengers that they are a weighty inconvenience for this first class aircraft and remove as much comfort as possible.
The Brain Bag fits perfectly under a domestic airline middle and window seat, but it might not on transcontinental aircrafts, even the biggest ones. The reason: the entertainment boxes placed under the seats which only allow a thin, square bag just like the Western Flyer and Tristar.
If you are forced to check your bag on the transcontinental flights, there will be nothing to protect the Brain Bag straps against abuse or destruction.
By contrast, on the Western Flyer and Tristar, the straps can quickly be stowed, your essentials (packed in the Packing Cube Shoulder Bag,, a Kit or a Medium Pouch) removed in seconds.
If you are lucky enough to keep your Western Flyer or Tristar with you, just slide it under your seat, fasten your seatbelt and you are on your way to Italian Adventures!