I got my IK20s from the US, like the ones here (the same seller that I used). Don't worry that it says ES300, the important thing is that it's 6 x IK20s, which is exactly what you need. I did a walkthough on changing plugs, which is in the Workshop forum.
I can't say I've really noticed any difference on my car, but then I didn't particularly expect to. Suffice to say that they're new plugs so should be better than having old ones in there, and maybe will very slightly help fuel economy ?