One area of difference between the two kick drum pedals are the beaters.
Let's look at the drum beaters side-by-side:
You can see that the Iron Cobra beater is a bit smaller than the Jr pedal and more adjustable. The Iron Cobra beater also comes with a small adjustable weight. I played with this weight in all different positions. Putting the weight at the top gives some extra power to your kick. Putting it at the bottom makes it a beat easier to kick. From there, you can move it anywhere in between or even remove it if you want.
Next, notice that the Iron Cobra has two chains and the Jr only has one, making it a bit less rugged. You can also notice the spot where the beaters insert into the pedal in the pictures.