TrackIR 4 or 5

I am wanting to invest in a TrackIR and I have a couple questions.
- Is there really a significant difference between the TrackIR 4 and the trackIR 5?
- Is it totaly necessary to use the hat clip thing? I have heard that some kind of reflective device would work also.
- Is there really a significant difference between the TrackIR 4 and the trackIR 5?
- Is it totaly necessary to use the hat clip thing? I have heard that some kind of reflective device would work also.