Anybody that is doing picking is measured by the number of picks per hour. It doesn't matter whether they are using Voice or Wearable or handheld or even Google Glass. The goal is to pick as many as possible of course with as less errors, no mispicks, no shorts, no picking errors at all. Also there are systems that can provide realtime feedback to pickers on what their target is and how they are doing against their target.
Typically Voice is faster because the picker doesn't have to constantly keep looking at his gun or wearable, he is getting instructions through the headset and has his two hands free, which enables the maximum productivity. But also Voice requires a lot more integration, meaning it takes more time and expensive to turn on (with an exception of some systems).
The best way to start measuring the productivity of any picker is Picks/Hour. The more they pick of course without any errors, the better they are.
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