The difference can be very large in the quality of them.

But also... most generic manufacturers are very lax with what they put on their labels.

The actual amount of protein you may be getting, may not be equal to the label or to other products.

And their processes are usually done cheaply.
Leading to most generic proteins to cause gastric discomfort. (bloating, gas, etc)

But if it works for you... then by all means.. use it.