I use the $5 plan. Basically for any time I’m searching for something I already know where to look (weather, sports scores, particular website) I use ddg or brave (or bookmarks). When I’m looking for more nuanced things like programming questions, recipes, reviews, etc. I use Kagi. Works pretty well with bangs in Firefox.
To answer your question: I hate ads so it’s worth it to me to have no sponsored crap in searches where there is something to sell
I think y’all are talking about different things. Some sites (like google) have direct yubikey support where you plug the key into the device and what you’re talking about isn’t an issue
Other sites don’t have direct support, but allow you to use any authenticator app which is what you’re talking about with using the yubico authenticator app/key combination. Plugging it into a yubico authenticator app on any device will show the codes
Unfortunately I don’t have an answer for a way to protect those other accounts. I guess the hope is that if you lose it, it can’t be tied to your accounts, just the websites themselves
Ive had two on proton mail (plus more on their services) without any issues