Both GK and I tried Cachya, and found problems getting it to work in IL2 - The main issue is that it takes mouse pointer control from the mouse all the time it's loaded, so if you've loaded the tracking program first (it doesn't work at all the other way round in any case), then your mouse pointer goes whizzing about your desktop as you move your head. This raises bigger problems in game with regard to scrolling and resizing the map for instance. FreeTrack solves that problem, but I was never 100% happy with the setup despite assistance from the erstwhile Jedi and others, probably had more to do with the way I built the headset than the actual system.
Despite the price, I haven't found anything that works as well as TIR, and with the minimum about of messing about too. Plug it in and hey presto!
Jabo