Well, it obviously works, since it alerted you to a potential problem. Whether it does any good depends on what you mean by that.
As you'll have seen from the link SpacePhoenix gave you, it works by checking the site against various databases. These are downloaded every thirty minutes, but there is nothing to say when they were last updated. In other words, the information could be out of date.
I would double-check the information - for example, through [SiteAdvisor, [URL="http://www.mywot.com/"]Web of Trust and [URL="http://hosts-file.net/"]hpHosts](http://www.siteadvisor.com/). Of course, you have to use common sense here. People are more likely to report a problematic site than a good one, so even if the site has cleared up its problem, changed owner or whatever, it may still be listed as problematic because all the reviews are out of date. Check the date of the most recent review for an indication of how up-to-date the information is likely to be.
Another good check is by a site:www.domain.com search in Google, which will display results with an alert if Google has detected a potential problem.
I don't know whether it has a feature like this natively, but you can get a Web of Trust extension for Chrome or Firefox, which will do the same thing based on the WoT database. I expect there are other extensions, too.