When comparing Razer Lachesis vs Kensington Expert Mouse, the Slant community recommends Kensington Expert Mouse for most people. In the question“What is the best gaming mouse?” Kensington Expert Mouse is ranked 55th while Razer Lachesis is ranked 74th. The most important reason people chose Kensington Expert Mouse is:
With thumb and pinky on the buttons and three fingers controlling the ball, the user's wrist lays flat on the table (or on the provided attachable wrist rest).
Specs
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Pros
Pro Braided cable
Helps prevent kinking, curling and protects the cable prolonging life of mouse.
Pro Ambidextrous
The Razer Lachesis is an ambidextrous mouse.
Pro Shape and size good for medium to large hands
The Razer Lachesis is a great mouse for those with large hands. With the hump where the users palm rest being a bit further back than a lot fo other mice it makes a good fit for those large hands.
Pro Custom color lighting
Using Razers Synapse software users can customize their color lighting.
Pro On the fly DPI switching
There are two buttons under the scroll wheel that allow for on the fly DPI switching.

Pro Comfortable and ergonomic
With thumb and pinky on the buttons and three fingers controlling the ball, the user's wrist lays flat on the table (or on the provided attachable wrist rest).

Pro Intuitive link between ball motion and FPS camera angle
The ball is large enough for turning it to feel like physically rotating an object.
Cons
Con Horrible lift-off distance
Lift-off distance is advertised as 1mm, which is not true, it's more than half an inch.
Con Unreliable drivers
The mouse freezes, lags and the mouse pointer might even die.
Con Unreliable CPI switcher
On-the-fly CPI scale resets, and sets to wrong settings often.
Con Not a mouse
This is a trackball, not a mouse.

Con Questionable secondary button defaults
The upper left button, which is the hardest to use, is middle click by default. The upper right, which the ring finger naturally rests near, defaults to Back. This can be particularly annoying as the Back button is easy to brush when moving hands between keyboard and mouse.
