According to the latest data, Valve has sold around 500 000 Steam controllers which isn’t exactly the best number. They have been officially selling the controller since November 2015. It’s been over half a year and what’s even worse the number also includes all of the controllers sold with Steam Machines (all of them have at least one controller bundled).
It appears that Valve’s hardware isn’t popular at all and it’s Steam OS is nearly dead. How do other controllers sell? In last 6 months around 10 000 000 PS4 controllers were sold.