This guy was the clip-on accessory for the Argus C4 or C44 cameras, though really you could put it on anything with an accessory shoe. Very similar to my Kodalux L and my Walz Corona, except this one is a lot smaller (about the size of my Capital). The bad part about being so small is the selenium window is about half the size of a postage stamp, which means it doesn't much power, so it's not very sensitive.

I was fortunate: mine came with the case and the accessories, so I have the little incident cover, and there's a place to unmount the foot and store it in the case. And I've got the booster cell (with the incident cover!), which makes up for the tiny on-board cell.