I use USB-C devices almost exclusively and opted the other way around, carrying a USB-A variant with a C-A adapter. A few reasons:

* The A variant yubikey is crush resistant and mechanically simple for a longer life.

* The adapter acts as a form of connector saver for my yubikey, since I usually keep it physically attached to the yubikey itself. With this approach both wear-prone sides (C male and A female) are on the adapter, which costs as little as 1/50th the price of the yubikey.

This is non-compliant to the USB specifications and potentially dangerous (as in, it could fry your hardware).

You might know what you are doing, but are you sure that's true for everybody who might find and use it in the future?

Please don't buy/produce these things.

I was looking into something like this, and while this probably works fine these aren't allowed under the USB spec, so you're hoping whoever designed these did it right and its not going to misbehave with some devices.