I have one.
It's really good for:
Streaming video and other stuff from your PC to your TV that doesn't work with Chromecast or your TV streaming thing of choice. Like some web players, or your music app.
Playing Steam games on a bigger screen, especially couch multiplayer games like Brawlhalla
Not so good for:
Streaming Youtube or other things that work well with Chromecast etc.
Playing Steam games with a lot of detail and action, like NieR: Autotomato. There will be brief losses of frames or quality even if you're connected by cable instead of wifi.