Yes, it's a three button mouse and those are seemingly as rare as hen's teeth these days, but you knew that already, indeed it is probably why you are looking at this particular item, so I'm not going to delve too deeply into that.
The third real button and lack of scroll wheel aside, this isn't actually such a great mouse. Build quality is perfectly solid but nothing special, and I'd like slightly more tactile feedback to the buttons. When I compare to some cheap Logitech scroll mice here that cost around a third of the price they come out level in terms of my impressions of their quality: both are perfectly serviceable but nothing out of the ordinary. For a mid-priced mouse such as this frankly I'd expect something a little bit better, but I suppose you do have to pay a premium for what is nowadays a more specialist item.
Ergonomically, again it's perfectly usable but not great: the "hump" of the mouse is both slightly too high and doesn't extend far enough back for my tastes, although if you're a fan of the Microsoft Intellimouse you'll probably quite like it. I would also have liked to see some depressions on the buttons to guide your fingertips into place: this mouse is regular width so dividing that width into three makes each button quite narrow, and it is easy for your fingers to drift out of the correct position for each button.
Ultimately then it's a fairly expensive but very ordinary mouse. I'm happy enough with it and I'd happily buy it again, but that is more down to your limited options for three button mice than this being inherently a particularly great mouse.