Ok, so I have to ask, WHICH TrackIR to get.
Four, five, or six? Any pros or cons with any of them?

I have 5, but I've had trouble with the Track Clip Pro (that doofer that clips to the left side of a headset). It is USB powered with three lights instead of simply being reflectors like the Track Clip that attaches to the bill of a baseball cap. My Track Clip Pro would simply stop working intermittently.

Another point to consider is the size and type of headset you routinely wear if you opt for the Track Clip Pro. I recently upgraded to a very nice over the ear headset with a headband too wide to accommodate the Track Clip Pro.

Cheers

EDIT: I could not find anything about TrackIR 6 on their website.

I have a 5 ever since it first came out and it has always worked great
I use the hat clip thing that I clip to a visor and no problems.

I use a "4" (with version 5 software) and hatclip, and it works just fine.

Same here! Point of note: always make sure you have no light coming in from a window or reflecting off of something behind you as that will fool the TrackIR and cause all sorts of problems. I keep the blinds down because of this.

Same here.

I have 5 now, I used TrackIR 3Pro with the Vector (hat clip described above) until recently. It worked great until the camera unit went out, but it was six or seven years old. The only real advantage to 4 and 5 is that their cameras have a wider view. So if budget is a concern and you can find one on ebay....

5 works great for me, didn't know there was a 6 out.

I use TrackIR 3 Pro with the Vector, no problems.

B.

I just visited NaturalPoint's website, and there was no mention of a TrackIR 6. Only 5 and lower was available to purchase in their store.

Honestly, I don't know for sure there is a 6 out. I was guessing because when I googled it, TrackIR 6 showed up in the possible results. Probably a false flag of some sort.

Thanks for all the suggestions.

Best is everyone has a closer look here:

NaturalPoint - TrackIR

Me too. The version 5 software works well with the 3. The only problem I have is that sometimes the reflections off glass pictures affects it during the day. But mostly I fly at night anyway.

Had a Track IR 4 with 5 software. Was okay until it stopped working half a year ago. Bought a Track IR 5 Pro, mainly using only the reflctor clips, and for me it is a huge improvement over the 4th version. It seems to be much more smooth and precise in response to the head movement. I would recommend this version therefore.

Regarding the sun problem, yes, I had this aswell with TrackIR 4, to the extend that I wasn't using TrackIR during sunny daytime, which I found quite frustrating. This is no problem anymore with version 5. There is a slider under the camera setup tab called "Light Filter Threshold" where you can tune down the ambient light detected by the camera until only the reflectors are visible. Works like a charm now, even with bright sunlight in the face, no need to delay some flying anymore-great!

Not sure, whether this option wasn't there in the TrackIR 4 version, must have been, since I was using the software edition No 5, but I haven't recognised it...