a) Avoid 1st generation. A flashlight is more useful.
I disagree with this, gen 1 works under many circumstances, but its not anywhere as good as the later & more expensive units. That was one reason why I asked about specific use, the Gen 1 is fine for looking about & moving about in low light. Its not really suited for the more advanced applications of NV though.
Avoid the el-cheapo Russian stuff, its pretty horrible for the most part.
Look at European Gen 1 because they developed gen 1 beyond US units as they switched to gen 2 instead.
If you're going for outdoor viewing then a good gen 2, or a European Gen 1 is what you want, but bear in mind things like:
Worn, or hand held? (Do you need to manipulate things?)
Single of true double tubes? (do you need depth perception for handling things, or will a single optic do ?)
Is near focus important to you? (distance is easy but you'll frequently need to adjust focus for close up)
Will you use them in low light, or no light? In no light you'll need auxiliary illumination, or thermal capacity (Mega-expensive)