Likely these are the "white label" drives you see on pricewatch, being advertised for 2/3 the cost of a new retail or oem drive. "Just like western digital, seagate and maxtor", blah blah blah.....
Bottom line is, they're refurbished drives. Thus the 30 day warranty on them, and also why they look new (is cuz they got cleaned up & shiny during refurbishment).
Chances are you'd likely get one or two bad drives out of ten, and get lucky with the rest. Question is whether they'd go bad before or after 30 days? If you look around on Pricewatch, you can find vendors (like 3Btech, I think?) that sell these, and will give you a longer warranty than 30 days, for around the same price. They're not the cheapest drives per gb, but they are inexpensive if you're looking for something smaller to put in a cheap build computer, where you don't care about losing the data, like maybe a child's computer.