Tweet This seems a much more civilized way to allow users to Tweet and Facebook your WordPress postings than Share This which includes a lot of tracking functionality.
After reviewing the code, Tweet This seems to do send nothing to or via any third-party sites and, unless configured to use a third-party URL shortener, includes no traffic logging click-thru tracking or similar functionality. It doesn’t appear to load any external .js either.
So, unless somebody educates me to the contrary, I’m going to call this ‘safe’ and leave it deployed. I hope you find it useful.