Knock Out has an extra set of hands and a bunch of weapons. I have not seen Prime in a long time, so I can’t honestly remember enough to tell you if they are accurate.
Knock Out looks great. You can’t see them from the front, but he has two more accessories, his wheels, which are pegged onto his back. They would not have fit on him in the box.
Overall: Knock Out looks great, and if you really like Prime, he’s probably a must have. For me, I would rather have more G1 characters.
Thanks for reading!