I do not use the app myself, but some friends of mine are crazy about it. They like it that you do not have to visit your accounts to receive messages most of all. Probably I should try it too.
At first I was confused by the title of the program and thought that it works only with twitter. So its functionality was a pleasant surprise for me. Even though I don't have a twitter account it was handy to work with Facebook through it, even though not all features work well with it.
It is useful if you do not want to open your browser every time to check the messages your friends on Facebook write to you. Or you want an easier way to post tweets. I enjoyed using the app, though as the author said the sending time delay didn't work well for Facebook account.