blue2002 and MtlTourist, you are right that the dimensions are slightly different than the US-norm.
Basically, the European & Asian Standard is a bit wider but less deep; the US Standard is a bit deeper but less wide. For international Travel, you may technically need our current Size rather than the US-Size.
Actually, the max size also depends on the Alliance. As far as I know, OneWorld has the US-Standard globally for all Airlines, but StarAlliance has the European size for all Airlines....

This situation is enormously frustrating both for luggage manufacturers and for customers. After all, our customers would need two versions of luggage to work on a global world and that is surely not helpful. This is the same situation for every luggage brand.
Solutions? Well, we could offer a luggage that is both less deep and less wide (the smallest common denominator), but that would seriously reduce luggage space. Not a good solution for frequent flyers who usually go carry-on only.

Other solution? Offer two versions like everyone else does -> yes we want to do that but it is not so easy for a startup both in terms of mold investments and logistics. But we WILL offer that.

The most practical solution?
Actually, the Plane designers are aware of that problem, and so most overhead bins have a real restriction in terms of luggage height (55-58cm), but there is no real close physical limit for the luggage width and depth. And as a result, almost everywhere you fly, you practically could almost always pack a luggage that is like the maximum common denominator of the two standards. Thats not the law, but it is a reality.

So the best thing, no matter what luggage you carry, really is to just smile handsomely to whoever checks your luggage size. Worked for me thus far, also in economy, especially if I travel only with a carry-on, which I always do.
Or buy two sizes, which makes me happy as a manufacturer but sad as a customer.