It puts it more in your face. Ecency just gives the notification. If you dismiss the notification then out of sight, out of mind. This tool is a little more focused on tracking the comments/replies, sticking them in your face so you don't forget, and facilitating easy replying all within the same interface.
I use my notification list on Ecency to comment and reply and see new posts from my favorites. I don't dismiss notifications until I have responded. Ecency works for me and I have no need for an additional tool.