As someone who is comfortable with TOTP but hasn't tried FIDO-/Yubikey-style devices, I have a few questions: - Are drivers for this already installed as part of desktop Ubuntu 20.10/Windows 10? Any driver installation will absolutely make this a no-go for family members. - Is additional software required for anything non-techies might reasonably want to do with this device, including resetting it, adding an entry or…
In general, you cannot (by design) back up these devices; if you could, that would defeat a lot of the security they provide. That means that if you lose it, you will have to find a way to get 2FA disabled for each and every account you enabled it for. Some orgs will have pretty onerous (but necessary!) processes for doing so, like having to provide government ID or physically visiting a brick-and-mortar location to prove your identity and ownership of the account.
Some sites will allow you to simultaneously enroll two devices, so you can keep one as a backup, safe somewhere (though not too safe; if you were to, say, put it in a bank safe deposit box, it'd be a pain to fetch it any time you want to add a new account). But many sites only allow a single device to be enrolled.
Some (like Yubico) let you purchase a "cloned" set of devices, where you can get two (or more) devices with the same keys on them, so you could actually put one of them in a safe deposit box as soon as it comes in the mail to act as a backup. That also solves the issue of some sites only supporting one device, as all of the devices in the set are effectively the same device. However, it doesn't appear that this is an option with the Solo keys (not certain of this; happy to be wrong about it; it's possible that you might be able to wipe the key material off new Solo keys and put identical copies of new self-generated material onto more than one key). On the flip side, if someone steals your backup key, it becomes harder to deal with the situation; with distinct keys, you can just revoke access to the stolen key. But with cloned keys, revoking access to the stolen key will also revoke the key you use daily.
I just wanted to bring this aspect up, because people unfamiliar with these devices need to understand the consequences if they lose their key; it can be a huge pain in the ass to rectify that situation. This might be an understandably big turn-off to non-techies who are just looking to add a little extra security, but not a big maintenance burden and difficult failure modes.