There are three trial versions. One for ZBrush 2021 second for ZBrush 2020 and third for ZBrush 2019 . Each is good for 30 days. While the full versions have just over 9,000 voice commands the trial versions have just over 4,000 voice commands. The 4,000 voice commands should cover over 90% of the voice commands you would most often use in ZBrush so you can get a real good idea if HMC Voice Command (HMC) is right for you.
Installation Video

Key for 30 Day Trial:

Key for 30 Day 2020 Trial:

Key for 30 Day 2019 Trial: