Yes, it's indeed overrated. However, there are quite a few advantages it has over the official Twitter app:
- thumbnail previews of pics in Timeline (that's a big advantage imo, so that you know right away what the pic is about and don't waste time tapping on it if you feel it's not worth it)
- "Load more tweets": if you are reading from below upwards, it will load the tweets *above* the tweet where you pressed the button, without shifting your location (official Twitter app will work this way only when you go from up downwards, and not vice versa)
- displays the number of unread tweets
- support for "Read Later", i.e. you can easily save a link to one of your favorite apps such as Pocket, Instapaper etc
- Mobilizer: you can choose between Google, Instapaper and Readability to display content, so you usually don't need to zoom in on the screen
- links in the Timeline are of light blue color, @names are dark blue and hashtags are light gray color: easier to distinguish altogether
P.S.: I e-mailed Tweetbot support the other day with the list of things that bother me (from my previous post), and they said one of the reasons you don't see some of the features (such as user's images in their account) is due to the Twitter API restrictions...