The ZH Cabin Bag is not top opening. I have the The Daily Carry-On with Pocket from Away, which is similar in that it is a clamshell, not top opening. If you use this style of bag, whether from ZH or Away (or even Rimowa's version) with the accordian style divider, its like almost top-opening in that when you open it, it can still stand up and you can put items in and out of it. This works better if you are using it to store a laptop, books, and papers, and less well if you are using it to store clothes, gifts, grocceries, or other 3D items. I like the Away bag and I like the form factor, but I find clamshell design limits its usefullness still I don't use it for transporting documents, so I understand the appeal of the Rimowa.

But the Aleon looks like exactly the alternative you are seeking --- it's a top-opening aluminium case of the same form factor, but at a much lower price and is actually available. It has free shipping and returns in the US so you can try it out. I generally prefer two-wheels to four-wheels on luggage, but for a case of this form factor four wheels is helpful for rolling down narrow airplane aisles.

This also looks like an alternative, from AliExpress. Cheaper, but no returns. I have had generally good experiences with AliExpress.

There are some even cheaper alternatives available on Amazon, like the ALUMAXX Discovery Pilot Case or the T.Z. Case International T.z Apl-410t Sd Wheeled Pilot Case. Note that these can be had on Alibaba for about $50 in quantity, so don't expect the highest quality.

Finally, do you really need it to be aluminium? The Parat 208.363.170 Pilot's Case is a really high quality polycarbonate case. It can be had in Europe on on eBay in the US.