I bought TrackIR 5 and the extra cost Trackclip Pro. Frankly, I don't use TrackIR much. I find Eyefinity drastically reduces the need. Having said that:
TrackIR 5 is a good product. Its easy to set up. Does what it says it will -- and very well (allows natural head movement up, down, sideways, tilt up, etc -- all work like real life -- they have a demo on line).
In my dark or semi-dark gaming area, the hat reflectors work very well; so, don't need the Trackciip Pro. The Trackclip Pro is less convenient than the reflector on the hat -- but might be needed in a well lighted area. One does have to use TrackIR a little bit to get used to that way of controlling the view -- because every little head wiggle wiggles the view.
Buying TrackIR and Trackclip Pro together resulted in a discount at the time. Price seemed reasonable for the quality.
Can't compare to TrackIR 4 -- as I don't own that.
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ATI Sapphire HD7970 OC - Eyefinity 5760x1200 24", 1xDell-U2410 H-IPS + 2xHP-ZR24w S-IPS, Extended 23" Samsung cPVA, Ceton InfiniTV 4, Bulldozer FX8150@4.5GHz w/Swiftech Water Cooling, 16GB GSKILL PC3 @1866, ASUS Sabertooth 990FX, Corsair 120GB SSD, WDigital + 3x Seagate + Hitachi + 2x WD Ext = 10.0TB, Sony DVD, OCZ ZX 850W PSU, CoolerMaster HAF922, TM Warthog HOTAS, TM T-Flight Stick X, TM Cougar+FSSB & CH Pedals, Saitek X52 Pro & Pro Combat Pedals, TrackIR5 w/TC Pro, Windows 7 HP 64b