I got a Steam Link and controller for X mas. I was initially super skeptical about the Steam controller but I feel most of the negative feedback it's gotten was unfair. I feel like a lot of people were expecting a controller that was better than a standard game pad and KB&M. Neither of those things are true and I don't think that was Valves intention. My experience with the Steam controller is that it is literally a Jack of all trades, and a master of none. That's not a bad thing because it's probably the most versatile gaming peripheral ever made. The level of customization on it is outstanding. There is literally nothing that it cannot handle on a PC as far as in input is concerned. With a little tinkering you can get it to do anything you can imagine.
The Steam Link also works exactly as advertised. I currently have it connected through an older WiFi router. There is a noticeable delay, although much less than I anticipated. There are also occasional graphical artifact and hitching. It works well for all games except ones the require super fast and precise inputs (i.e. Meat Boy, Downwell, Crypt of the Necrodancer). I suspect when I run cable to it it will work great.