I have this one and I use it exactly as you describe, when 2 card are connected it recognise them both as separate drives.
So I can backup my camera photos (SD card) to the micro SD card just using my phone via the USB C port. Then I can connect it to my desktop computer with the USB A end.
Ooh I like the idea of the micro reader with a/c/micro! If I keep a card in it it can act as a thin drive and become multipurpose!
Edit: I did some AliExpress digging and found this thing that looks like a pretty sleek solution https://a.aliexpress.com/_mq2Ck8i
I have this one and I use it exactly as you describe, when 2 card are connected it recognise them both as separate drives.
So I can backup my camera photos (SD card) to the micro SD card just using my phone via the USB C port. Then I can connect it to my desktop computer with the USB A end.
Quite a nifty device
https://www.amazon.co.uk/UGREEN-Card-Reader-Memory-Adapter/dp/B07ZKRM12C