Yes, that's true about the Erika being smaller than it first appears in photographs. In reality, the height and length even of the long model hardly exceed the dimensions of the Colt 1908 .25 vest pocket or most other vest pocket pistols. The Erika's slender, protruding barrel and grip create the illusion of a pistol more spindly and ungainly than is actually the case.
And, when we get around to thickness, or thinness, I should say, it really takes the cake; the Erika has to be the absolute thinnest semi-autotmatic pistol (relative to its height and length) ever made. I just can't think of any other pistol that is as flat and thin as this one.
Jim, you mentioned that the Erika's curious feature of a non-grip-contained magazine was common for pistols of that era. But the only ones that come to mind are some of the early designs like the Bergmanns and Mauser Broomhandles. As far as pocket pistols go, I know of no others that have a magazine located outside the grip - indeed, it wouldn't seem a very logical design choice, since the objective in defensive guns is usually to make them as compact as possible. Are you aware of any other relatively compact early semi-autos that utilized this feature?
For all its unconventional appearance and magazine location, the Erika's internals are anything but groundbreaking; it's pretty much a direct copy of the Clement pistols (the 1909 specifically), with a post-driven hammer, separate breechblock with a stud on top that engages the action rod, etc. The resemblance is extraordinary on a large number of points and certainly cannot be coincidental.
RSVP2RIP mentioned that he bet that 4.25mm ammo probably cost about $40 a round now. He's right on the money, as the only 4.25mm round I was able to locate cost me $35 a couple years ago.