Surely the leds are important but silver or copper is a matter of taste. Also if your tonearm internal/external wires are copper what's the point to use silver led wires in headshell or vise-versa? If your cartridge coil is copper why you need silver wires or vise-versa? Some of the best tonearms use one set of wires from cartridge to your phono stage.
About Audio-Technica headshell with fixed screw holes:
Yes there are no slots to move cartridge in headshell but on the backside of the AT Technicard or Magnesium headshell you will find at least two sets of mounting holes. The most important thing about this type of AT shells is FULLY ADJUSTABLE OVERHANG AND AZYMUTH and with thus option you don't need any slots, you move the whole shell to adjust cartridge with your protractor!
About Audio-Technica headshell with fixed screw holes:
Yes there are no slots to move cartridge in headshell but on the backside of the AT Technicard or Magnesium headshell you will find at least two sets of mounting holes. The most important thing about this type of AT shells is FULLY ADJUSTABLE OVERHANG AND AZYMUTH and with thus option you don't need any slots, you move the whole shell to adjust cartridge with your protractor!