Why should they send you more for free? How do they know you didn't eat it? They don't. What you experienced was one of the known risks you assume when dealing on the internet. They said they'd even cover the shipping! Your post should've said "Performance is great! They screwed up, but it's not going to cost more than few minutes of my time to make it right".

That said....keep it and use it. It probably won't kill you.