In the years before fixed clips came along, there were various ideas to make pens portable. That most of them sold so well makes it clear that people wanted to bring their pens with them when they left home, usually to be used at work.
The Swan Metal Pocket was one of the most successful of these innovations. It was sturdily made from pressed steel and bears the Swan logo on the part that would appear outside the pocket, so acting as an advertisement too. That the Conway Stewart version was so similar suggests that they were both made by the same company contracted to produce them.
Though they are anything but ephemeral, being durable in the extreme, to a collector they would count as ephemera. They could, of course, still be used for their original purpose but a word of caution is required here. Many have succumbed to rust internally and will scratch a pen. It is possible to restore them to use with emery cloth or wire wool