Well from the moment I pulled the Lachesis from the box I knew this mouse was going to be the one I settled on. Some of the newer mice are too light for me. The Lachesis was weighted more and I favored it right away. I found the layout to be comfortable, more comfortable than the Copperhead in fact. The bump forced my hand to rest on it in a more comfortable position and I liked the fact that the body of the Lachesis was longer. It fit my hand better than both the MX-518 (which I have used for years) and the Razer Copperhead.