My experience with thermal scopes is limited to 2 models from Torrey Pines, now Sector Optics (a subdivision). The T12-N I've used for a few years, and like it well enough as a hand held spotter for rats. Tried it on a low powered .177" airgun but found it was impossible to make consistent hits on rats even at 5 yards, just too low resolution for precision. Then I bought a T20 with 3-5.5x optical zoom and a higher resolution screen. Tried it on the ratter, made a few hits, but just as many misses at 7 to 10 yards, so gave up and again went back to my cobbled together 3x scope with a Carson IR monocular, the IR emitter wired so it's in an offset tube above the scope and with a lens to focus the beam for further range. No problem with that rig taken down rats with head shots at 20 yards, though most rats are taken inside 10 yards.
The T20 now lives on my PCC as a backup, with a 45 degree offset QD mount. Zeroed to my scope, it's good for maybe 12" groups at 50 yards. Good enough I guess. I wouldn't recommend the T20 for hunting, but in a pinch it makes a heck of a good thermal viewer, easily picking up a warm car engine or disc brakes a couple of hours after the car was used and making such objects generally identifiable. It can distinguish between most men and women in general form at 100 yards. At 20 yards it's good enough to pick out facial detail differences. Not state of the art, but cheap as these things go at around $1,000, and ruggedly built. I swap between a couple of CR2 rechargeable batteries, and it's good for a couple of hours per charge. Here's a pickup truck at night about 30 yards from my workshop window, an hour after it parked:
This link should play a short clip showing the T20 in use on an airgun, knocking down a 5cm aluminum disc (heated with a small torch) at 7 metres. the diagonal scan lines aren't visible to the eye, rather an artifact of recording the screen with a digital camera:
[video]http://www.luthier.ca/other/forum/T20_on_5cm_warm_target_at_7metres.mp4[/video]
