Does it still work with the clip from the TIR 3 Pro? I don't wear a headset...
Is the clip that you're talking about the one that clips onto a baseball-cap visor? If so, then it should work, since the TrackIR-5 Pro comes with one of those at no additional charge. Believe it or not, I never had one of those for my TrackIR-3. I was putting their little silver stickers onto the end of my headset's speaker arm for tracking purposes which actually worked OK until just recently when it became erratic.
The "Clip Pro" is something you pay extra for (NaturalPoint has a bundled package that includes it) but it's pretty nice. It clips onto your headset (so, yes, you would need a headset) and then connects to the TrackIR via USB (but they've designed it so that the TrackIR only takes up one USB port on your computer).
If you've never tried flying with a headset, you should try it. I started doing it several years ago and have never flown without them since. I find it to be much more immersive...like you're in the cockpit.
P.S. Perhaps the best thing about the TrackIR-5 and RoF is the "six degrees of freedom" (i.e., the ability to lean forward in the cockpit or lean left and right out of the cockpit). Takes the immersion to a whole new level. I can now lean forward into my gunsight for better aiming, just the way pilots probably did in real life.