My opinions...SNAP is the easiest to get used to, PAN is the most intuitive/realistic, in a multiple con environment I get less disoriented with my hats since I am sooo used to them, I have slowed my TIR3Pro down as far as I can go and it is still a little too fast for my taste, the amount of IR radiation that the device sends out in a thousand years is probably in the neighborhood of a Saturday afternoon mowing the grass with your shirt on.
TrackIR is an awesome product, their tech support is really responsive and personal over at their forums. The device takes some getting used to though, and it DOES suck up some CPU cycles, so if your rig is on the edge for FPS already this wont help.