The Steam Link is a decent product that does more than people realize. On the surface it allows you to connect your PC to your TV over a wireless connection. It then connects to your TV via HDMI. Honestly there are other items that can do this and some of them go far beyond steam.
Valve recommends that you use one of their controllers or connect some hardware via the USB ports on this unit. That is where some people walk away from this product. First - there are people who really don't like the Steam controller. Second - why would I want to connect a wired product to this? The whole point is to connect your PC without wires.
Here is what Steam does not tell you:
1 - Most wireless keyboard / mouse units work just fine with the Link. 2 - Most bluetooth hardware works with the Link.
What does that mean?
Most of your wireless hardware will work with the Link, including...the PS4 controller.
Yes if you want to use a great controller that does not need dongle, you can get the PS4 controller up and running. To do it, use another wired or dongle item to navigate the Link menus to the Bluetooth options. Kick on the pairing. Hold the "Share" button on your PS4 controller until it shows up on your Link. Pick it on the Link. Done!
It works great. The only real functionality loss is the rumble feature. If that's a big deal then you might want to try a different solution.
Overall the Link does more than Valve lets on. You can use far more than Steam hardware or wired hardware with it.