Bought kone xtd a year ago. Been happy with the mouse and even not using all its potential. But lovely mouse, good, big sized mouse, can adjust the weight, mouse 5 button, my 2nd fire is in just great position , at the end of my thumb, and it looks great.
My preferences if buying a mouse:
Size - to fully fit my hand, as many of them are just too small, narrow.
Shape - will my palm feel good on it.
Weight - can I adjust it.
What's inside - dpi, sensor type, options to modify.
Mouse 3,4,5 button layout, position, acces.
The surface "pads" - the quality of the surface pads or whatever they are called.
Manufacturer - never would buy a mouse from a small company, trust issues you know.
Feedback - always would google the shit out to find all pros and cons.
And finally the looks, who gives a shit about the looks? Your mom who would be only girl that comes in your room for the next 10 years?
