This little oddity comes all the way from Sweden. Strivel is apparently a word-play. The first part of the word comes from the Swedish word for Strap which is "Strigel" and the second part comes from "Rakhyvel" which translated is razor - So "Strap Razor" OR "Honing Razor"
Its made of pressed metal and has "RostFritt Stal" stamped at the top of the handle. Its a one piece that the top flips open. The handle is a Diamond Knurled hard plastic outer covering and they came in a variety of colours. The blade tray has a spring arrangement to hold the blade in place.

So how do you strop it? Insert the blade, close the top cap, extend the mechanism and run it up and down a few times and its supposed to hone the blade. When you work the mechanism it runs the blade from side to side, honing the upside of the blade on the upstroke and the bottom side on the down stroke.
The first question that I had was - how effective was the stropping mechanism? - I tried with a used "current" blade and it didn't do very much, if anything at all.
They were supplied with thicker blades, so they may have been able to be stropped. The other advantage of the thicker blades is thet there would have been more adjustment. With the blades of today, 3 is the highest setting before it gets too loose.
It was patented in Sweden back in 1949.

When you do find Strivels, they mostly are non-adjustable. From what I've seen, the non-adjustable ones don't have the hard plastic handle.
The first picture below shows it with its very cool case and picture 5 shows a close up of the adjustment dial.