I've tried this burrow from them: http://www.petsmart.com/product/index.jsp?productId=3039693

There are two issues I had with it. One is that is only covers half the cage. So you need to fill the other half with substrate to level it off. It bugged me but wan't so much a problem.

The other was that Mojave got lazy. She stayed in it for days on end without ever coming out. She'd get a drink and ran back in. She never hunted crickets, just waited for them to be adventurous and come down to her. After a month she just looked fat and lethargic. I'm sure she was happy just to sit there and be hand fed but I didn't think it was healthy so I took it out.

She's on tile now and really seems to be the happiest with it.