I was being peppered with failed logins, always from foreign countries. This app blocked them all! 100% successful.
FYI, I use All In One WP Security, which shows me the failed log-ins.
The only caution: When you click "select all" on the country list, it also selects my own country! (although there's a note saying it won't select your own country) - apparently there's a small bug there.