These machines had no electrical components, opting for a stove-top as the power source to create the steam required for espresso with later models adding a steam wand for milk texturing.
While they wont be suitable for regular duty and almost any espresso machine today will put these to shame with regards to consistency and quality of espresso, I think they are romantic and nostalgic. If I owned one I can guarantee it would take pride of place in my home.