So why are they so useful? It's the "hollow shaft" part that does the trick. Rather like deep sockets can do some things that ordinary sockets can't, they'll let you loosen/tighten a nut that's threaded way down on a long bolt. And the hollow shafts on these extend the entire length of the shaft.
If you look up the shaft, you can see all the way up to the handle. It's not just a 2cm recess, the entire shaft is hollow, accomodating anything up to that length. For example, using these tools, it's easy to install long-shaft controls in panels and neatly tighten the nut without fighting with pliers, trying to keep a box-end wrench in position on a thin part, or running the risk of marring the panel.
That's one, on the right, in position to tighten the retaining nut, quickly and easily.
Recently, I realized that a metric set of these would be a very useful thing to have as well, so I went out to see what the offerings were. I was pleased to find out that the original Xcelite HS618 set is still available, as well as the individual drivers. It's nice when useful things are still in production, after all these years. Unfortunately, they don't seem to offer a metric version.