I got this as a replacement product from my defective G403. Both mice had exactly the same problem. When one scrolls in one direction, the mouse scrolls in the opposite direction randomly (Sometimes almost 50% in the opposite direction ...). It happens when you scroll slowly and quickly. I cannot possibly give the product a rating other than 1 because it is extremely frustrating to scroll at all, which makes the mouse unusable for me.
There are quite a few threads on Logitech's forum about this particular problem. So it seems like a pure lottery if you get a mouse with a working scroll.