Jim,
Downside is that there are so many variants some poor and most really unsafe and bad.
The one I refered to that comes in a canvas grey bag, was made like a pistol shape and the lower and upper casing cheap plastic which encased the tube.
The downside was with them when we measured the radiation omitted from it at the Home Office, more was coming back into the users mark one eyeballs than where it was supposed to be going out the front.
Sadly I gave my notes on the variations they were offering the Russiantroops in the 70's away when I stopped lecturing on night vision. Peter L may have a view on them, but I know they were banned for Police and Military use due to Health and Safety risks to the users.
I only refer to the 1st Gen kit not the later 6M 2nd Gen updated and more ruggefied casings units.