They were meant to be a 1-shot , a filler for Showcase #37. Destroyed in the story, they weren't intended to live again. But when the writers couldn't come up with a new idea (trying out new ideas every 3-4 issues in Showcase...no wonder Brave & Bold switcxhed from Showcase format to team-ups of established characters [the pseudo-science was very bad) and then to Batman team-ups), Metal Men went 4 issues, and finally won their own comic. It never grew popular enough,tho, to warrant 8 ,let alone 12 issues a year.
I have a family portrait somewhere where everyone has big goofy grins. I remember when it was taken, too. The whole living room was turned into a big photography studio. I wanted to include a plushie Incredible Hulk in the photo, but mom wouldn't let me.