It's actually (like much of what Steve does) a really good idea; high mass, sticks to the pole piece really well as-is, extends and linearizes the magnetic circuit, looks nice, readily available, comes in sizes to fit any pole piece, the cheap part actually preferable (lower steel, no trademark).  Steve is not a dumb guy.  My only problem, as with any phase plug, is that I love my FE168Σ's so much I can't bear to take the X-acto to them.

Whatcha working on?

Poinz