Generation 2+. Upgrades, with benefits.
Second generation image intensifiers, variously referred to as Gen2 and Gen2+ are essentially upgrades to the earlier Gen1+ S20 image tubes that preceded them. The changes that have significantly improved their night vision performance include a thickening of the tube's chemical coatings and the introduction of a thin glass micro-channel electron amplifier plate.
In combination these two changes not only dramatically brighten the images you'll see through these revamped Gen2+ S25 tubes, they deliver virtually distortion-free images that are much sharper and better resolved.