As seen on the box, the Konix Speedking was produced specifically for use with the CPC+/GX4000.
However, it is unknown what makes it CPC specific...? Is it a two-button joystick...? Or even an analogue joystick...?
Note: Konix has produced one-button and two-button joysticks, as well as digital and analog joysticks. But it's unknown if/which of them were CPC compatible.