No one seems interested, but for reference purposes, I thought I'd post an update. I've had them on my bike for about a month now and haven't had any problems. The price is way less than anything comparable, yet they don't seem to have any quality issues.

I bought 4 tubes, including tax and shipping, for under $15. And, if you're a weight weenie, they do weigh the advertised amount of 100g per tube. Highly recommended.