Not for mounting a desk! For things like pictures where the stress is mostly shear (downward force), you can use something as simple as an angled nail and hang five or ten pounds of picture frame on it. Wall plugs, especially the ones that expand behind the wall, do provide better resistance to pulling force. But these desk brackets will have a LOT of pull applied to them because of the leverage of the desk surface.

Some plaster against the ribs of that plug are not enough; it will likely yank out of the wall and may take a chunk of wall with it. In older plaster-and-lath construction, you'll most likely crack/damage the plaster from the flexing caused by the plug pulling against the lath in the wall.

As the original article says, you'll want to hit a stud, and IMO even that (alone) is not enough for this kind of application.

If the old apartments in Germany are anything like those in Belgium, the inside walls are probably plastered brick (or worse - concrete). Wooden houses are a rarity here. Living in old buildings I've never encountered one of these walls built around a wooden frame.

Yes, they are mostly plastered brick.

By the way : concrete isn't bad as you think. There are different type of concrete.But... While it's strong and resistant to fire, if you live in somewhere where the earth quakes are common, concrete is a bad choice. Also metal frames in the concrete is problematic, they have to be resistant to the water (galvanized etc.) or in time they will rust and tear apart the concrete.

America vs Europe.

In America most houses are wood, and I don't mean log houses.

And there is no way wall plugs would work in that kind of American wall.

In Norway and Sweden we also have mostly wooden houses. I would imagine it's the same in Finland as well. Probably because we have lots and lots of trees here, compared to continental Europe.