it’s great to hear that you got your mom a PCEye Go and I hope that it works really well for her.
The PCEye Go is a device from Tobii’s assistive product range which includes Tobii’s software for controlling the Windows environment using your eyes only. The EyeX Controller, on the other hand, is an eye tracker which is part of the EyeX development kit–it isn’t a product in itself. And while it does include some software, it is mostly of interest to developers–it cannot be used to control the windows environment out-of-the-box.
Also the packaging (software, level of support, etc) differ significantly.