The 50/1.4 Nikkor-S is a good lens. It's not exactly the same as the AI and AIS versions, since the lens elements are thicker in it. Same optical design, though. I like them enough that I'm about to build one good lens out of two marginal lenses.

Note, the Nikkor-S lenses are not AI in the true sense of the name. They've been AI'd, but with a factory conversion ring, instead of milling the original ring. Even with the 50/2 AI, you may wind up getting an AI'd lens through KEH. It'll look the same externally, except for three things. Firstly, the rubber focusing grip will be shinier and with smaller ridges. Secondly, the serial number will be below 3,500,000. And, thirdly, the lens speed post that factory AI lenses have will not be on the baffle around the rear element. Because of that, if you attach the lens to an FA or an F4, there will be no matrix metering.

Because of that, KEH's nomenclature is misleading. With certain lenses, like the 85/1.8 "AI", there were no true AI versions. Nikon did sell them with an AI aperture ring at the end of production, but they didn't install a modified baffle with the post. So, every single manual focus 85/1.8 Nikkor is AI'd, if a camera shop or seller refers to it as an AI lens.

-J