I'm using one right now, great mouse. As far as it being "heavy" goes, the weight is adjustable using the supplied weights and the weight cartridge. It can go from very light to reasonably heavy depending on your preference.
If you have a claw grip, it's a great mouse. But if you have a palm grip (IE your palm touches the mouse, or if you find this most comfortable) I'd advise going for the G500, i have one and love it, so comfortable to hold and it also has adjustable weights, i prefer mine heavy.