Hi Laurel,
 
I know that the Ferret Store sells them also.  I have not bought one (yet!)
but they sound like a really neat contraption.  Since I do not have one,
I cannot tell you how they work or anything.  I just know that the Ferret
Store whom I trust, recommends them for ferrets.  If you get one, let me
know what you think of it and how well it works.
[Posted in FML issue 3180]