While the interface for TweetSmarter needs some clean-up, it does offer some interesting help to your tweets. You use the site to build your tweet and it sends you and that content to the Twitter homepage. They dodge the bullet on you handing over your password that way, which is ingenious enough. I would suggest logging into Twitter via the browser first, then jumping to this service to say the later log in step.
Not all special characters work in all clients and browsers, so they let you hover above them to see the limitations. I did laugh at their explanation of the black boxes for tweeting. It makes it look like a government doc or you are hiding profanities. Interesting way to act like you said something but didn’t.
The last part is the ability to add a retweet link to your tweet. I am not sure the benefit of a link where most people now search for RT or retweet and you have to sue extra characters. I might have to play more with this one to get it.