[Radio Wrangler]

Be a little cautious, Ferrites and Iron dust mixtures are quite different beasties.

On the whole, ferrites have higher permeabilities but offer worse stability.

Ferrites can be used in inductors needing some accuracy, but they rely on the shape including a well-defined air gap in the magnetic path... EG a gapped pot core. Without the gap they are good for RF transformers and decoupling inductors where their value need not be accurate or stable.

Iron dust has effectively a lot of air gaps distributed throughout it. Complete toroid cores are popular in RF work, and have no machined gap at all. Inductance factors are reasonably reliable and the stability is good enough for VFOs.

In coil formers like the Denco ones, high frequency ferrites will not be as bad as you might expect, because of the significant air path. The air path dilutes the overall permeability of the magnetic path, and the permeability of air is very close to that of free space, and is very stable.

Unfortunately a lot of people just aren't aware of the extent of the spread of properties of these materials, they just see something grey and crunchy. I've found it to be the root cause af various people's disappointing projects. There are also mumetal dust toroids and epoxy-coated tape wound iron toroids out there waiting to catch the unwary.

David