The negative comments are not based on the performance of the Calonox (I'm sure it works fine), but on it's price compared to other thermal front add-ons which have the same or better performance for significantly less money
As I said, buy a thermal from a well known optics manufacturer (Leica, Zeiss, Swarovski) and you pay a premium for the name, but gain nothing in performance
Thermal is now very competitive with prices relative to performance coming down all the time and new entrants coming into the market regularly
At my last count there were well over 120 different models of hand held thermal on the market from 13 or 14 different manufacturers
Since Leica (nor Zeiss or Swarovski) don't actually make any of the critical components (germanium objective lens, thermal sensor, signal processing electronics and display) none of their traditional expertise is of much use to them
They obviously see a market for thermal products and want to get in on it - but the only thing they have is their brand, they have little to no in house expertise in the manufacture of thermal products
Cheers
Bruce