A while ago, I did a quick explanation of how the tv-advertised housevalues.ca works. That post is here, or see below. Now there is another ad airing for a site called justlisted.ca. What's it all about?.
Same company, same deal. It's a US company whose product is leads for agents. So yes, you can sign up for new listings to be emailed to you, but you will also be immediately contacted by whatever agent has purchased the rights to your area.
You can get the same information from the local agent of YOUR CHOICE. Any Toronto Board agent can set up a "match" which will automatically email you listings or changes that match your criteria -- criteria much more refineable than the justlisted.ca options. They aren't evil, but you should know what you are getting into.