This is tangentially related. The U.S. Coast Guard trialed Safran ECOTI and the Chinese InfiRay Jerry C2 as thermal clip-ons to NVGs. The results show that in scenarios where there is sufficient ambient light, the clip-ons didn't bring enough additional benefits to warrant their use. However, in search and rescue scenarios far from shore, where ambient light levels are low, they proved very effective. Although ECOTI is superior on paper, the soldiers preferred the InfiRay for its ease of use and clearer thermal image. I'm sure the Coast Guard will find InfiRay far easier on the budget as well.