I am not saying I am a fan of TwitReply for what it does. It takes much of the human side out of any interaction. While in customer service worlds it may have an immediate benefit until they realize it was automated, much like email systems do.
What the tool does it scan the Twitter stream looking for keywords and then sends a reply with some custom tweet, including links if needed, in reply. The author is reported to be in Italy, and I hope they consider oAuth or some other form of authentication than asking for your username and password.
There are some rules, such as you can’t create a rule that sends more than 5 tweets per hour and the reply you create will be reviewed by an actual human. But when this grows too large, imagine the complaints of spam that might be generated?
There are better ways to monitor and respond to your company or product mentions. Hire an intern in social media for starters.