I decided to pull out my metal-toed original (left) and bootleg (right). The bootleg has had Rumble (well, Frenzy according to reprolabels.com) applied, so don't pay attention to them.
Notice the obvious difference in the rivets. The plastic color difference may not be as apparent, but the bootleg has a lighter shade.
The original has light blue hips, while the bootleg has dark blue. These can be
barely seen in the Frenzy auction too. Look at the knees and around the hip stickers.
The elbows and feet are super-chromed on the bootleg. The silver face paint on the bootleg is shinier as well. I don't think it shows up in the picture, but the original has fairly detailed hands while the bootlegs lacks this detail.
Lastly, giving the two a shake test, the bootleg is super rattly while the original feels nice and solid
Disregarding the decals, the bootleg is identical to the one in the auction.