A final update:
I ordered and tested the Zipulses connected to a cheap "pulse sensor" (for waterflow through a pipe) in my "lab" (= at my desk 
) and the Lixee Zipulses does work. I assume it works with any "normal" pulse sensors (based on the "Hall effect" = a magneto-electric pulse), there are a lot of them available on Amazon/AliExpress.
One caveat though: when I tested it by blowing air through the sensor the Zipulses lost counts if the sensor was spinning very fast. This is in fact normal, because of how the pulse counter logic works: a pulse consist of a change from an "off"-state to an "on"-state (based on a cut-off if analogically determined, which is what the "Hall effect" is), an interval in the "on"-state and a change back to "off"-state. If the sensor spins too fast all the single pulses will merge into one long continuous pulse because there is not a clear enough "off"-state.
This is also why there are so many different sensors = you need to select a sensor with a "spinning interval" that fits your situation/what you want to measure (in "pulses").
The next step is ordering a large-ish diameter pulse sensor and "adapting" it to work in a natural stream (as a paddle-wheel sensor). Winter is coming, aiming to have it in place in spring.
