Here's Knuckles in his box, so you can see that the box is the same for all the plushes, and has some nicely chosen oldskool stock art and checker patterns to go along with it.
Here's a good close up for their medium Knuckles, out of his box. It's a good solid plush with decent construction as well. The white chest stripe is a bit low and huge, but that may be due to the overly-round body they're using on him here. His fists seem an OK shape, but his face is pretty nice. For his shoe-soles they've used a type of fuzzy fabric, which seems a bit of an odd choice here. Still, if you want a good classically styled Knuckles plush, GAME is likely the best bet for good price, and the ease of finding it.