Blacklist Monitoring is only monitoring if your website gets blacklisted by Google's Safebrowse list. If your website gets blacklisted your customers can't access it anymore through most browsers. Even worse is that it will be eliminated from search results within the search engines as long as it is blacklisted.
Blacklist Monitoring does not protect you from malware and hacker attacks. Blacklist Monitoring is only recommended as a supporting product to website security protection.