Planetary gear reduction
The problem with planetary gear reduction is that many times they aren't sized properly for the job they perform. If your application imparts more torque to the planetary gears than they can handle, they will suffer an early failure. If you see a lot properly sized planetary gear boxes, they are often much larger than you would expect.
The starter for sale in the link above does not have planetary gear reduction, just a basic 6:1 reduction, it appears to have reduction with a timing belt and pulleys.