I just bought one of these, brand new + sealed and everything. It's at least 15-20 years old and obviously works flawlessly with a USB-ADB adapter (Griffin iMate).
I always loved this keyboard when I was in middle school & high school and some Macs in the lab had them. The Apple Design keyboard that followed sucked, as did every Apple keyboard afterwards until they moved to the low-profile scissor switches.
I thought that the Extended II would boost my already fast typing speed (100+ WPM) but it hasn't—the extra throw of the switches (almost 3x that of my MacBook Pro) negates any benefits the nicer feedback is otherwise providing. It's better than the Matias TactilePro I had a few years ago (cheaper build quality than Apple's, and louder switches even though they're supposed to be the same).
I'm enjoying this Extended II and feel it was worth the $120 it cost me on eBay (cheaper than it was new when it came out!) but I do think the cult of mechanical keyboard junkies will eventually disappear as those people literally die out (or their keyboards, I suppose). Unless you grew up on a mechanical keyboard, I don't think any user accustomed to keyboards of the last 5 years (Apple ones, at least, since that's what I mostly use and they're quite good) will see any benefits to using one. They're louder, way bulkier, and can only be used when connected to a computer via this weird and ugly thing called a "cable."