Well chaps, there it sits, attached to the bottom of the monitor. It arrived a day early, and I've spent a couple of hours trying it out in MSFS. First impressions are good - it works straight out of the box, downloads the software when you first plug it in, and is a doddle to set up and calibrate. I have it plugged into a USB port at the back of the monitor, but it comes with an extension lead to go to the PC if needed. The mounting can be adjusted to tilt the Tobii unit up and down
MSFS detects Tobii straight away, and is configured using sensitivity sliders. RESET and On/Off can be mapped to the keyboard. Performance in MSFS is every bit as good as TrackIR. Much more natural, in fact, because it tracks both eye and head movement. So, your eyes move first, followed by your head - just as in the real world. As an example, when scanning the instruments, you just move your eyes, and then maybe your head a little to look out the left or right windows. You don't have to point your face at things, as you do with TrackIR. That said, you can adjust the percentage combination of eye movement and head movement: move the slider all the way to the left, and it will only follow your head, move it the other way and it will only follow your eyes. It'll be interesting to experiment further with that combination.
I had a problem with looking down ( pitch axis ), but I adjusted the angle of the monitor, titled the unit up a little, and re-centred it - all sorted. There are some reports that it has difficulty when you are looking directly behind you - as you would when "checking your six" in a combat flight sim. I have no problems whatsoever - in fact, such are my initial sensitivity settings that my view goes well past the 180 degree mark, almost round to 270 or 90 degrees, depending on which way I turn my head.
Another thing that people have pointed out is that the view isn't steady enough when programming an FMC -there are too many minor movements from eyes and head. Well, that's no different from TrackIR in my opinion. I always paused TrackIR when doing anything like that, and the same can be done with Tobii.
The biggest advantage is the obvious one - no hat and clip to wear, no emitter contraption on the side of your headphones, no cables, nothing. I often didn't bother with TrackIR when flying for an hour or so because I couldn't be bothered with all the paraphernalia. With Tobii, you just activate the app, and you're ready to go. I haven't used it in any other game yet, but will try it in Arma 3. It works in P3D and X-Plane, by the way.
I've yet to come across any real problems. These might surface as I use it more, or in other games, but so far I'm very pleased with it. And, because of the convenience, I'll be using it a heck of a lot more than TrackIR.