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I've never understood why germanium diodes are special here.

Am I missing something? Does the diode have to be germanium for this trick to work?

The lower the voltage drop, the better. I guess, in their part of the world, germaniums are cheaper than schottkys

Simple: The germanium diode was the first suitable diode I found in my parts collection. :-)

A regular silicon diode will not work. An appropriate Schottky silicon diode will do the job; see the Infineon app-note in the "PPS" of the website. Also, the point-contact (regardless of the semiconductor material) reduces the diode's junction capacitance, making it faster, i.e., more suited for RF applications.

What's the typical forward voltage of the germanium diode vs a silicon diode's 0.7[V]?

It's a neat hack! Long live the Rigol DS1054Z!

I didn't measure it, but literature has a value of about 0.3 V for a germanium diode's forward voltage.

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