We were both skeptical, and don't quite understand how it works, but it really makes a huge difference! No robot with a digital compass should go without it.
If µmetal tickles you, try Metglas
I stumbled over a page comparing several of these mag-shielding alloys recently, but now I cannot find the link
very good, but there are several alloys that shields much better than that...Here
is a page selling various types (not as expensive as you seem to think, or as I would have thought) and the page is a good read even if you don't wanna shop.
As far as I've heard, the difference between iron and µmetal is close to yhe difference between µmetal and Metglas, so you don't need to add much weight shielding a motor (if you don't mind the bill).
The only disadvantage of the stuff is that its like 10x more expensive than other metals . . . there are different alloys and thicknesses, but you can expect ~$40 per square foot.
The exact reason I didn't brought up the subject of "super" mag-shielding alloys a couple of weeks ago - I would have thought them a bit too expensive for hobby work (although I have to admit that I wasn't a pro back when I first used it, for screening a mains transformer in a sensitive audio pre-amp).
But it seems it's possible to get it and still retain your soul
Just too bad they won't export Metglas
Btw, I have an old recording studio mixer (all the modules, less the frame) and several of them are wrapped in µmetal IIRC (except the mike pre's, they're wrapped in silver), but it would be a shame to strip that (and I'd rather find a cheap source for the Metglas locally, if that's possible).