Speed Check is a browser extension that displays unwanted advertisements while surfing the web. It also changes the main settings like the new tab address and search engine. It promotes fake software updates, tech support scams, and other schemes. The add-on is already removed from Chrome and Firefox web stores.
These kinds of applications often have dedicated websites that promote them. This one claims that it tests the loading speed of any website. It is unknown if it is actually functional or if it shows random results on the screen. Whatever the case, it is hard to see the reason why someone would need a plugin like this.