Well, he said his friend found the artifact dangerous, so I wouldn't think it was something generally benign like either mind-protecting helmet. I suppose if you assume the Crimson Gem of Cytorrak is addictive, it might be a dangerous artifact. But actually, thinking of supers with addictive artifacts, Spidey's alien costume comes to mind. It's something clearly advantageous to have, but (hello, Venom) clearly also a danger to use.
I think the only other super-accessory I can think of off the top of my head that someone might want but whose super found dangerous would be Black Knight's sword (didn't that threaten to possess him, too)?