These are the official controllers for the OneGX. They snap onto both sides of the UMPC and basically turn the OneGX into a portable gaming machine.
The analog stick and the buttons (two shoulder buttons and four face buttons) feel fine, the DPad however is not very comfortable to use.
As most games use analog sticks these days, this shouldn't be an issue for most users - but if you plan to mostly play games using the DPad, this controller is not for you :)
The controllers connect themselves using Bluetooth and can be used as two single controllers (similar to how the Nintendo Switch Joycons work).
They can be charged via USB (unfortunately, the OneGX cannot charge them), but as the battery lasts pretty long, this is not a huge issue.