If that's all you're using it for, you'd be better of with Hipchat, which serves as a functional notification channel and from what I recall is free for <10 use

If that's all you're using it for, you'd be better of with Hipchat, which serves as a functional notification channel and from what I recall is free for <10 users. I guess Slack would be worthwhile if you're using it for multiple projects, though.