Yeah, if you wanna buy a webcam just to use it with FreeTrack, there is no need to buy such an expensive one. If you remove the filter, you won't be able to use it as a normal webcam for usual video purpose, so it's not much of an interest...
If you want to get the best tracking ever and you're ready to spend some money on it, you should buy a wiimote
.
By the way, I guess this webcam will work since most of the Logitech's have been reported working with FreeTrack.
Rémy