But to get back to the original topic, yes there's a difference. Buy two cogs a cheap stamped and a machines and try them out for yourself. Ask someone with a kilo Tt if you can borrow their stock cog for a day and I promise you will be rotafixing it off 20 mins after you put it on. I have a salsa chainring, the cheapest BMW chain the lbs had and a surly cog and ss locking and my bike makes next to no noise, and it takes me 8 miles each way to work everyday and for fun rides on the weekend. These were among the cheapest parts I could buy and they work flawlessly and the cog shows no wear from the last 8 months of use