I jumped on the sale of the Tempest at newegg and just plugged mine in. It feels wonderfully smooth once you dial down the sensitivity, but there are some things that bother me coming from the mx510.
There are no "quick scroll" buttons to the top and bottom of the wheel.
The thumb buttons (which I had grown used to using while surfing) are extremely awkward. Not unusable, as I think the grip can be adapted to press them with the side of the tip, rather than the pad of the thumb, but definitely less intuitive.
I'll give it a couple weeks before a verdict overall, but my initial impression is that while it may be a better gaming mouse than logitech, the logitech is probably a better surfing mouse.