As the site says, the device can only withstand a few months of sustained use - which is a pity.
EDIT: Thanks, jpatokal, that cleared things up.
As a practical demonstration of this, there's an ancient ferrofluid exhibit (80's?) at a local science museum. While the fluid itself kinda-sorta "works" in that you get the pretty spiky shapes when zapped with an electromagnet, the edges and bottom of the glass case are thickly coated in viscous black gunk.
I think that the ferrous particles in ferrofluids are mere particles. They'd have to be very, very small to be classified as nano, and we've seen before that making particles of an ordinary material that small can change its properties, ala "transparent titanium dioxide".