Yes, my hardware keys work on my mobile devices as well.

> do you now need to maintain two keys for every service?

I do maintain multiple keys for every service. I wouldn't say it's a lot of maintenance, any more than a far more secure "remember me" box is "maintenance".

When I register for a new service, I add my hardware token on my keychain as a passkey. I sign in on my laptop for the first time for a service I'll use there more than once, I make a passkey. I sign in on my desktop for the first time, I make a passkey, maybe make a spare in my password manager. Maybe if it's something I use on my phone, I'll make a passkey there as well when I sign in for the first time. When I get around to it, I'll add the spare hardware token I keep in a drawer. But its not like "I just signed up for a new service, now I must go around to every device and make a new passkey immediately. As long as I've got a couple of passkeys at registration time, I'm probably fine.

Lose my laptop? Its ok, I've got other passkeys. Lose my keys? Its ok, I've got other passkeys. My laptop and keys get stolen at the same time? Its ok, I've got other passkeys.

Its really not that hard.