I tried the free version of BulletProof at the suggestion of my hosting company to ward off a DoS attack.
The plugin is rich with features, so it's somewhat hard to set up.
I quickly upgraded to the paid version. Support by Edward Alexander, the publisher, was outstanding. He patiently went through a long trouble-shooting process with me, and kept me informed of what was happening and the changes he made to the site. He also suggested a number of configuration changes and gently pointed out that I had too many plugins running, which slowed the site down.
I can't rate Edward, BulletProof, and his support highly enough.