I would not buy three vor four expensive SD cards, but rather an external SSD. The 4TB models are pretty affordable and would offer plenty of storage. Micro SD cards are more expensive per TB and can easily snap when handled poorly.
Downside of the external SSD approach is that you cannot charge and play at the same time, so you would need to copy a game from external storage to internal before starting to play.
I feel this, however, as you alluded to, there is no product they I'm aware of that attaches nicely to the steam deck, that has a 2280 slot, and has PD passthrough, and a stand. If you find one I'd love to know about it.
The SD cards are a nice touch for us anyway because my girlfriend and I can swap games without having to sacrifice the whole SSD.
Plus these were roughly 54 dollars each. Not horrible considering the cheapest 4tb nvme is 150. So I'm not sad about it.
Nice find!! Yeah I haven't had any issues with them for gaming. I only hit the order button when I saw a reviewer say it worked just fine on the steam deck.