Very easy to implement; if it doesn’t work, check your system clock!

I had absolutely no trouble integrating this plug-in with the regular WP login. We’ve set it to enforce 2FA for anyone with editor role or above, leaving it as an option for regular members. The one time we had any trouble, it turned out to be that the user’s system clock was about 15 minutes off, far outside the grace period for TOTP! I almost regret that the free version does everything we need. I did have a small bit of integration trouble with one highly customized area of the site which turned out to be me not understanding something fundamental to WordPress… the issue I raised in the support forum was handled rapidly and considerately.