I have the Mamba and I was using a Logitech G5 before and this is a real improvement. The Wireless is great and has never run out on me. It charges from the usb even when pc turned off. You can't change the weight on it but this hasn't been a problem.
I should add that is very fast and great for First Person Shooters. I have to turn the dpi down quite a lot or it's just too fast.
Thanks for the reply on the Mamba. Do you notice any lag or skips at all when using the mouse? Also, when you plug it in to the USB, does it just give it power and still transmit wirelessly, or does it send signal through the USB.