1. you really should explain better than saying that Copperhead is better just cos you're using one.
and this is from RAZER's own mouth themselves, who recommend Diamondback over copperhead for FPS.
both mouses are good in FPS, but there are still complains from those very low sens FPS users on Copperhead.

2. just cos something is more expensive, doesnt mean its better.
refer to above.
Death Adder's sensor, which is an upgraded version of the Diamondback, is actually aimed at those very low sens players.

i have both Diamondback and Copperhead.
i also play alot of FPS.
but i use Copperhead more, because it feels better.
and since my sens isnt extremely low, i dont feel the issues that those ppl mention.
and i dont like Death Adder, cos i dont like right handed shape mouses, simple as that.

slow sens? low sens.
i guess you dont play FPS much?

well, again i guess you dont play FPS that much.

its actually easier to aim and track with low sens.
and since its so low, to turn real fast you have to move the mouse real fast.
thats where a good sensor comes in, so the cursor actually can handle that fast movement without skipping.