Bruno28.
I own the ARGUS 4 -160 and the ARGUS 4 -HR320.
As you will know, they are designed for fire fighting. As such they are deliberately fully automatic and have limited fasciitis. Image quality is excellent. They are not the best choice for general work.
The Keysight cameras use the same A-Si imaging sensor technology but also provide manual focus plus lots of measuring capabilities. The U5855A is a 160 x 120 pixel camera so the ARGUS 4 -HR320 does provide clearer images with its 320 x 240 pixel sensor array.
The ARGUS 4 series also has some great options like Wi-Fi and IP camera operation, but these are expensive to buy. I have the Wi-Fi optional module but will be converting a battery pack to provide the Ethernet IP camera capability and external power input. It makes a great surveillance camera
The FLIR E4 was a good option at Round $700 as it could be upgraded to full 320 x 240 resolution plus additional menus. With the release of the latest 2017 revisio, such is currently no longer possible.
Fraser