I'm also a Freetrack user with a DiY ballcap (with IR leds from Radio Shack) and a $10 webcam from Fry's (that I removed the IR filter from and replace with a small piece of floppy disk substrate). I've used it for years and it works great on every flight sim I've tried it with (RoF, FSX, DCS, BMS).
I dabbled with Opentrack a few years ago, but I couldn't get that to work right (it was on Win 8.1 at that time, so who knows if that was problematic?). Anyway, I switched back to Freetrack and it works just fine (I'm on WIn 10 these days).
In the very early days, I also used FaceTrackNoIR for a little while with just the webcam to introduce myself to head tracking. It worked passably well (any of the LED solutions will be better though) and convinced me that head tracking is a "must-have" for me, and prompted me to build the rig I use today... I had published an article on our New Wings website about it, but that article got eaten up in our site crash in 2016, and I've not recovered it from the old forum wreckage.
In any case, if you have some simple electronic skills, it's pretty easy to build, set up, and use. The LED's cost a buck or two each from Radio Shack (you can probably find them cheaper online), and everything else was already lying around in my "junk box", so the cost, in my case, was under $20 total, and an afternoon of tinkering around to put it together.