I bought these to replace the original pads on my PX100 headphones which had crumbled away after about 4 years of fairly heavy use and a year of storage. I searched for original replacements and found some online retailers selling a pair of original pads for about £6, excluding the cost of delivery and up to 12 day shipping! That's when I decided to go the 3rd-party manufacturer route.
You get 3 pairs of pads, packed neatly in a small plastic bag.
The foam is a little thinner and smoother than the foam used in the original pads. They are also a bit bigger than the PX100 earpiece, so they don't sit as flat as the original pads do. Finally there is a thin seam running around the edge of the pad, as these are made from 2 pieces of heat sealed foam instead of 1. These are the 3 main differences between them and the original pads. That said, the foam is not uncomfortable on my ears. Yes, these are bigger but not so much that they'll come off during normal use. The collar is actually quite snug, it's the main flat bit that sits between your ear and the earpiece which is slightly bigger. And the seam is only noticeable on closer inspection, just reverse the pad and the seam is gone. The only people who'll notice they aren't original are probably audiophiles and Sennheiser fanatics.
These negatives (if you can call them that, they are 3rd-party after all) are really minor and don't affect the useability or sound quality of my headphones. They may not look and feel like the original Sennheiser pads but they are not supposed to. What they are is a good cheap alternative to a pricey original accessory.