Gen 0 is what is worthless. It can only work with an IR illuminator, and is so bulky that its not even sold or made by anyone I know of. Its late ww2 tech.
Gen 1 is your Nam era technology that can use starlight/moonlight and an IR illumination. It is grainy and the versatility of it is limited, but the newer Gen 1 types are apparently better than the old starlight scopes in resolution and sensitivity.
Gen 2 is your late 70's tech and is a great leap forward in sensitivity, resolution, and versatility.
Gen 3 is 80's tech that was product improved in the 90's to some degree.
If all you can afford is Gen 1, its not the worst thing. But it has its limits. If you can live with them, its useable. Shotgun news tested a new Gen 1 rig a month or two ago and said it was serviceable but if you could afford a Gen 2, to got for it.