I'll reaffirm the claims that adjustment is everything.
I've had TrackIR since v2, and now run v4. If you don't have it yet, I highly recommend the 6-vector setup. Not only will it make the whole thing that much more intuitive, but then you can duck when someone shoots at you!
Keep working with the deadband adjustments, as well as the aggressiveness curves. These are critical to getting a response curve you are comfortable with.
When it's not right, the thing can feel like a real burden, and slow you down. When you begin to close on a config that suits you, you'll know it.
I've never had a motion sickness problem, although my wife can't even watch the screen when I fly...with or without TrackIR. Seems people can either process the visual images independent of coordinated balance cues from the inner ear, or they can't. If not, you'll feel ill.
Also, consider mapping the TrackIR enable/disable command and the centering command to your stick, so you can switch around quick. I find that I prefer to go back to a typical headlocked position when actually shooting, while using the TrackIR during acquisition.
Luck!