I've had a patchy relationship with A4Tech mice.
My first modern one had 3 buttons and the 2 wheels in a diagonal arrangement, with the top wheel acting as a middle button. After setting it up at home, I soon found out that this arrangement made the middle button very difficult to press. It was simply too far up to be of any use and couldn't make up for the added convenience of a second wheel.
So I switched to another A4Tech with the normal single wheel arrangement, but with "800 DPI precision". After a few weeks of very comfortable and precise use I started getting tracking errors on the vertical axis. The mouse cursor would jitter up and down slightly even when it wasn't moving.
So far, I haven't encourtered any major difficulties with my new A4Tech 800 DPI optical mouse. The tracking is pinpoint accurate and it even looks somewhat exotic in silver and black. I think I've finally hit gold this time. All without spending any more than the cost of a single MS mouse.
"Nothing livens up a robotic hymn of doom more than an amazing pair of jugs." - Brak