Well, so could a simple whitelist filter. But anyway, if you want to check it out and see what it's all about then head over to the site where you can sign up for a free test email account.
I think the Web site itself needs some help as I had trouble finding links to login to my account. You can login to your test account at this link.
Consider trying it for a while. Here's an idea: Post your free email address to a bunch of newsgroups and message boards. That ought to draw plenty of junk mail your way ;-) See if you can filter all of it 100 percent of the time. After you test the service post your comments below to let us all know what you think about it. Is it really junk-proof?