Questions

Hi.

Some don’t, other do.
So far, the ones on my own website target only wp-login.php.
Anyway, this is not a problem anymore, since the version 1.1 of this plugin.
V1.1 changelog:

New: choose what to do when someone attempts to access the administration area.

You can redirect them to a 404 or the front page if you want.

For the log-in plugins, I suppose it depends. I guess my plugin won’t work with those who create a new login page. Those who add a new action to the login page (Login / Register / Lost password / New action) should work.
The only way to find out is to give it a try.
To make it short: this plugin uses the real wp-login.php file.