Never heard of Pro Viagra as such. If you mean to say generic Viagra,then

1] Both generic and brand Viagra gives same effect, both differ in price. Generic Viagra is cheap while brand is costly.

2] You require prescription for brand Viagra while generic doesn't require prescription.

3] Generic Viagra has more chance of showing side effect, while brand has less because you acquire Viagra prescription once doctor recommend you based on your health for brand Viagra.