I've been a web host and sysadmin for 15 years. I'm skeptical when it comes to security tools, and many of them out there are either bogged down bloatware, don't do enough, or try to do too much (WP Security Ninja does veer slightly into that last category, but if you're going to do it well, I won't stop you).

Do I trust any plugin to be my entire WP security stack? No. Nobody should. That's like locking your door but leaving every window open.

Do I trust WP Security Ninja to be a crucial part of that security stack on an application level? I do, and many of my clients are better for it.

It does what other login security products promised they would, but it does it better.
It does what other application-level WAFs said they would do, and it does it cleanly.
It does what other scanners say they'll do, and does it quickly.
It does not guarantee you'll have no holes in your security, because Lars and his team know better.
It does as complete a job as a WordPress plugin can reasonably be expected to do.

Y'all do need to tune down the level of followup emails after every... single... installation... but I love you all the same. <3

-A