I am not talking about the USB-C adapter itself (or it's specification), but rather the physical properties casing of the Nitrokey 3A that you decided to use on the 3C as well, the thick casing is likely to be blocked by smartphone cases, before the USB-C adapter could enter the phone's USB-C port, however for reference you can use Google Pixel 6 and the Spigen Liquid Air case. The Yubikey 5C NFC has a part of the key which is thinner, ensuring that it does not end up being blocked by a phone's case, wheras the Nitrokey 3C does not seem to have any such thing, and that is what my concern is about before I would consider purchasing one. (I prefer not to use NFC for OpenPGP/PIV/OATH, hence why I did not purchase a Nitrokey 3A instead) Apologies if the description may be insufficient, I cannot provide a better explanation, being limited to words.