I have recently purchased Track IR.
I would say it's a nice addition to the game, but not essential.
Pros:
TIR is easy to learn. I had some trouble getting used to it after years of using the mouse stick on my throttle. However when I invite newbies to fly, they get TIR intuitively. Mouse view was always a confusing challenge to them.
TIR will improve your immersion.
TIR 5 is nearly plug and play. There are tons of customizations, but I'm ignorant of them.
Cons:
TIR is expensive! Your buying a $150 head-mouse.
TIR will not improve your aim. In fact it'll probably have the opposite effect. At least at first.
You have to wear a silly hat like this:
This is a TIR lan party.
If you've got the money, TIR is awesome. But a decent HOTAS and pedals are prerequisite. It will make you happier, but not more skilled.