With Google Alerts, you are likely to get dozens of emails a day, often with unwanted or junk news. This is especially true if the company name is a generic word (e.g., Plenty or Cozy). Rooster filters and organizes the news, so you don't have to wade through a ton of unwanted items. In addition, Rooster checks company websites for changes - that's often the only way to track what a company is up to.
Try Rooster alongside any other service, and you'll see the difference.