I finally signed up for LastPass Premium after years of using the free version of that password-management service. And I’m starting to regret that expense even though $2 a month should amount to a rounding error.

Instead of that minimal outlay, I’m irked by LastPass’s implementation of the feature I had in mind when typing in credit-card digits: support for Yubikey U2F security keys as a form of two-step verification.

Two-step verification, if any reminder is needed, secures your accounts by confirming any unusual login with a one-time code. The easy but brittle way to get a two-step code is to have a service text one to you, which works great unless somebody hijacks your phone number with a SIM swap. Using an app like Google Authenticator takes your wireless carrier’s security out of the equation but requires regenerating these codes each time you reset or switch phones.

Using a security key–Yubikey being one brand, “U2F” an older standard, “WebAuthn” a newer and broader standard–allows two-step verification independent of both your wireless carrier and your current phone.

Paying for LastPass Premium allowed me to use that. But what I didn’t realize upfront is that LastPass treats this as an A-or-B choice: If you don’t have your Yubikey handy, you can’t click or type a button to enter a Google Authenticator code instead as you can with a Google account.

A LastPass tech-support notice doesn’t quite capture the broken state of this user experience:

If multiple Authentication methods are used, only one will activate per login attempt. If you disable one, then another will activate on the next log in attempt. Because only one activates at a time, you cannot have multiple prompts during the same log in.

The reality you see if you happened to leave your Yubikey at home or just have your phone closer at hand: an “I’ve lost my YubiKey device” link you’re supposed to click to remove that security option from your account.

This absolutist approach to two-step verification is not helpful. But it’s also something I should have looked up myself before throwing $24 at this service.