As others have said, it would be useful to be able to select a WHITELIST of countries and have the plugin select the non-requested countries automatically. It would also be easier to have certain "geographic zones" selected with a single click, rather than having to select every country individually. I have chosen NOT to downgrade the plugin for this shortcoming.
The tools area was useful in discovering that many attacks are launched from countries I would have considered "safe", and leads me to make a suggestion for an improvement.
Would it be possible to use crowd sourced feedback from all the copies of this plugin installed worldwide to collect a list of IP addresses that routinely probe WordPress backends, and use that information to SUGGEST IP addresses that should be added to the blacklist, regardless of country?