WordPress.org

When i activate the plugin, the hidden fields are visible!

Make sure that the template you are using calls wp_head before the closing HEAD tag. See http://is.gd/tazh for more information.

What is the difference to other anti-comment-spam plugins?

Spambots are stopped within the plugin. You don't see them and most important you don't have to moderate them!

Does the plugin block Ping-/Trackback Spam as well?

No, the plugin focus on automated spambots only.

What about false-positives?

Due to the functionality of NoSpamNX false-positives are nearly impossible. There 'might' be problems when using WordPress Cache-Plugins, but none have ever been reported. If you are uncertain, try puting catched Spambots in moderation queue or mark as Spam.