"Accordion players usually need two straps, as the instruments tend to be quite a bit heavier, and the action is different - they don't need to push and pull so frequently, it's more of a steady heaving in and out."

Trust me, if you use Bellows Shake Techniques, you are throwing the box around a lot more, and need good properly fitted straps even on very small boxes - I had proper fitting and real straps fitted to my tiny Chinese 8 Bass to allow me to do lots of interesting things.

Not all Accordions are big, my 8 bass is very small, and my 32 bass fits in an airline carry on bag for those long international flights, as long as the rest of the passengers don't throw you off the plane.....