I just got a set of 20" DWS 06 from Discount Tires for $241/tire and $279/tire, front and rears, respectively. Installed after tax was a little over $1,200. That's not too much more than those off brand eBay tires you listed.

As for the tire warranty, the manufactures usually half the warranty if you're running a staggered setup.

Edit: Nevermind, just noticed the eBay tires were for a set of 2 each. The pricing just seems too good to be true, especially for an unknown product.