Wow - not a lot of people actually bought treadmills, I suspect. Nothing about this seems suspicious to me. They are always dirt cheap because they're bulky, hard to move, and about 90% of the people that buy them quit using them within a couple of weeks of purchase (typically if someone sticks with a workout for 6 weeks, they'll stick with it period).
As far as using one. Upside is convenience, especially if you live somewhere like Chicago where the winter's get seriously cold or there's a lot of snow. The downside is that they don't work as well as running because they help you along - if you ever run outside again, you'll discover you're not as good as the readout tells you. Still better than laying off completely until the weather improves.