Also, what is the difference between the above gear drive vs other gear drives?
Strain wave gears have practically zero backlash and high torque density (i.e. torque per unit weight) compared to other solutions available. Gearbox weight is important in articulated arms, since it adds to the weight of each link in succession. The extra weight means that each actuator must provide additional torque to maintain a specific speed target, but higher rated torque requires more gearbox mass, which increases the torque requirement, etc., etc. Ultimately, the arm speed ends up getting limited.
Strain wave gearing were invented in the 1950's. There are a couple of start-ups working on alternative solutions today, but they are still the most popular high torque density solution on the market that has near-zero backlash.