Did not see anything about the EyeX here on the forums so I decided to give a quick first impressions as I got mine yesterday.
Tobii EyeX Controller > http://www.tobii.com/xperience/products/
The EyeX device itself feels nice and solid built. It mounts to your monitor with a small self-adhesive steel bracket (comes with two) and the device itseld attached via magnet. But the device also has two threaded holes, so you could build you own mount. This might be needed if you are sitting to far from your monitor and your eyes would be out of the detection range.
What did it cost:
83,00 EUR - Device with a 30% coupon
20,00 EUR - Shipping
25,75 EUR - VAT
Did not have any problems installing and calibrating the device. And overall I am pretty impressed with how it works. Even though I don't have much use for it except for ARMA3 and I 'll put up a video of how it works in arma later. But honestly I bought it just for A3.
Also I had some trouble getting it to work with A3 in the first place as it needed a edit in the A3 userconfig file as described here: https://www.youtube.com/watch?v=zJdO2qeZn3A
In Windows 8.1 you can only use the eye tracking to warp the mouse cursor where you are looking, for Win10 there are some more features.
And if you are wondering: it works with glasses (you may need to clean them, as i learned ...).
A quick video of the tracking on desktop and in arma: