I bought the Advantage1 in 2008 and it's been one of my best keyboards ever since then. It's extremely comfortable. I wrote up a few paragraphs about my impressions here:

http://therandymon.com/index.php?/archives/167-Typing-in-Sty...

The one common complaint is that they had used rubber keys instead of mechanical for the function keys. Looks like that issue is addressed in this second edition. For sheer key build quality, the Totally Ergonomic Keyboard is better. But the Kinesis is more ergonomically comfortable, and includes a couple of USB slots so it can function as a hub (few other ergo keyboards do that).

I won't buy this new version because my own Ergo will probably last another 20 years - it's built that strongly! - and the rubber function keys don't bother me a bit.