When one thinks of Magneto as a character, his helmet stands out for being the defining piece of his outfit. The helmet is there to keep all those pesky Psionic characters out of his brain. To that regard, it is mostly thematic that the helmet gives him steady. Sure, he can still be confused or stunned but it requires extra effort on the part of the villain. The bonus kicker with the helmet is that it generates a resource for a Magnetic card. It drops the cost of his most expensive cards down to 2, which gives a 5 card hand a bit more flexibility, especially since you are usually using his pull to get a Magnetic card back.

Depending on your aspect build, it may be more important to get the Cape out before his Helmet but I think having a resource generator out early on in the game is a better long term play. Put on the Helmet and play the Cape and Armor for cheap to make Magento the Master of Magnetism that he is.