When a League streamer installs the extension, their audience will be able to pull up an interactive panel that displays the match scoreboard, the streamer's gameplay stats and match history, as well as other information. The interface features four tabs, the most notable of which breaks down the streamer's champion build (seen above). This part of the extension allows you to see the order the person you're watching upgraded their skills and runes, as well as what items they bought. One of the nifty features here is that you get to see a timeline of the streamer's item build, so you can get a sense of when you should aim to acquire certain items. The utility of the tool is that you can glean a lot of useful information about certain aspects of the game without having to wait for the person you're watching to say something.
At almost any time of day, League of Legends is one of the most popular attractions on Twitch, so it's easy to see why the company went out of its way to build this tool. With the game slated to make the jump to Android, iOS and consoles later this year, it will probably get a lot of use soon.