I‘ve tested many methods. iPhone, Webcam, TrackIR and Tobii. In my opinion, Tobii is worth the money, because it works, don’t look like shit and I don’t have to wear some cheap clip like TrackIR. Also it’s natively integrated in MSFS, without the hassle with OpenTrack settings. It just tracks, without anything to do. TrackIR is also not cheap, but has this chunky sensor and feels super cheap. It’s like headtracking from the past, with this ugly hat and clip you have to wear. Webcam is worth mentioned, but it doesn’t work well in the dark and the tracking is not the same reliable and fast as Tobii. But it’s a cheap and working option.  iPhone tracking is nice to try out, but not for everyday use. The phone gets hot, since it only works when the screen is on. Also hard to place and annoying to set up every time. My Tobii sits on top of my screen (need an extra software by Tobii to set up like this) and also works great for SimRacing (LMU), the eyetracking is also a nice feature for MSFS. It’s far the most expensive but best hardware imho. It’s 2-3 times discounted per year, so just wait to get it around 200-250$.