The Warpsmith gets Mechadendrite Use, but in what form?

Your pick either Utility or Combat-Forgot the correct term

Utility is for mechadendrites such as servo arm,inbeeded auspex, Medica/Tourture mechadendrite and so on

Combat is obviously for ballistic mechadendrite and the things that youl find in the tome of decay for those are for combat

So for any talent which has multiple possibilities, the choice is up to the player?

In this case yes youl either have Combat bionics or Utility bionics

THOUGH you can have bionics that works both ways such as Ballistic mechadendrite,Servo Arm and the mechadendrites inside Tome of Decay