I have had a TrackIR 5 since pretty much release which I used religiously for flight siming. I also have a tobii eye tracker. I have pretty much stopped using the trackir entirely now in favour of the eye tracker + opentrack. It is incredible, works flawlessly. You have a very small amount less horizontal turn tracking, but honestly your head has to be comically side on for you to notice the difference. Perfectly smooth and predictable. Lately been using it in Nuclear Option and it’s changed the game. TrackIR also works great, and is also flawless, but the key difference is the eye tracker requires zero hardware on your head to work. Even works through glasses.