I used it last night to do the Night Stalker mission and it made the world of difference.

Prior to using the set , I was belly crawling past the guards but unless I remembered to press the free look key , whenever I tried to look right or left to check their orientation to me I guess my feet stuck out or something and they'd open fire. Reload and try again.

With the TrackIR I was able to keep an eye on them over my shoulder with no problems and whenever I noticed them turning in my direction I would freeze. Was a whole lot easier. Mission success.