An absolutely great plugin. The plugin fits the use-case of adding twitter meta data perfectly. Further, admin settings and per post settings are integrated to enable customizing the twitter data.
This solved a problem for me, which was customizing the image per post. Sometimes the featured image can be large, or not the right dimensions. With this plugin, I can add an image with different dimensions and set the meta data to that image easily.
I scanned the code, and found good organization and naming. Although there is a PHP section which creates a HTML comment naming the program and author, I found nothing that would show up in the browser to website visitors or cause connections to outside servers. So basically, just a clean comment demarking the start and end of the plugin.
So I give this program a score 5, as it works great for the purpose, and doesn't seem to try to take over the web server or visitors browser to meet the goal.