I bought this keyboard a few weeks ago as I have developed a problem with RSI in my shoulder and arm. I had already tried a cheaper keyboard that was supposedly ergonomic but made the problem worse, so I forked out the hefty price for this one out of desperation. I'm very pleased I did - although it's expensive, it's a whole lot cheaper than treatment for RSI and it has definitely made a difference.
I found that it took me several days to get it adjusted perfectly and I had to raise my computer chair in order to sit in the correct position (as the keyboard is higher than a regular one). It's fairly easy to adjust - I've seen a review elsewhere in which someone complained about the large lever that is used for this, but it's easy enough to operate and you only need to use this when you're first figuring out the right position for it. As soon as I had the keyboard adjusted correctly, I found it remarkably comfortable to type with - surprisingly so since it looks a bit odd.
The keyboard as a whole is reassuringly sturdy. As it claims, the removal of the numerical keypad on the right makes it MUCH easier to keep your mouse within reach if you are right-handed, which is essential if you have problems on this side. There is an option to press a number lock and use some of the central keys like a numerical pad if you really want to.
In terms of usability, it does take a bit to get used to the location of a few of the keys. I found I could carry on touch-typing right from the start without any difficulties but it has taken me a little bit to get used to the location of the delete, backspace keys etc. For some of these keys, I now use a different finger than what I used to as the tilt of the keyboard also makes a difference in how far you have to reach.
So in a nutshell, if you have RSI or are keen to avoid it, this is an excellent investment so long as you're happy to make the effort to adapt to the slightly different feel and layout. I don't think I'll ever be changing back!