The guys at PCGamer was impressed with the SteamLink device but wasn't too blown away by the controller... it seems its not as good as a dedicated gamepad nor able to compete with the mouse, so it doesn't do either as well as the current devices.
Sort of you can use it as a mouse but its like a bad mouse device, and you can use it like a gamepad but its not as 'comfortable' as a 360 pad, so you really would be better off using the proper device for the job rather than the Steam Controller for both.
Mind you they did say it could just be a issue of getting used to the odd system rather than the system is actually bad, you know what players are like with change.
Sometimes keeping an eye on your stats is not a good thing
Some things are painfully obvious, others must be made obvious... painfully