I've never had the lens, but it's the first in-lens motor versions by Nikon. The AFI motor is not the modern sonic ring type, but a micro motor. I tried a longer version of an AFI lens a while back when I rented one and found it to focus pretty much as fast as an AFS lens, but others might have a different experience.
The issue I've heard is the lack of parts if the event that an AFI motor burns out, but this is just heresay via various forums. You might want to Google it.
Had them all...AF-I's the sharpest 300 next to the VR lens and only slightly slower to focus. If you find one that's mint it is an amazing lens. Something I really like (and many don't) is that it is very heavy. This makes it very resistant to vibration and that's a big plus when I'm working with the tc's. One of my favorites and great with all three tc's. Yes...you take a risk with parts no longer being readily available, but that's a choice.
I found what I would label as a mint++ AF-I for $2250 today. Actually, if one didn't tell you thatt it was used, you wouldn't know. All of the accessories are still in unopened plastic.
