Between the device and a real life piece there is a big
difference. The device can keep it hard and firm for as long as the
battery life allows whereas the real life piece is subjected to
individual endurance.
Furthermore, once battery life is spent, it is a simple job of
putting in new batteries not taking more than 5 minutes whereas for
a real life piece, it will take normally at least half hour or more
before it can be fully hard and firm again.
Further furthermore, the device can do rotating and sliding in and
out motion depending on the switch whereas the real life device is
depending on the skills of the performer.
Further further furthermore, the device length and girth can be
chosen carefully and then bought whereas the real life piece length
and girth is subjected to the
performer capability.
Given above reasons, the device win over the real life piece hands
down. Of cuz there are more reasons but I leave it for others to
elaborate 
