I've been interested in these for a while now, ever since the big splash (heh) from sharrow marine a few years ago, heres a link to some data they've provided comparing their prop vs a standard one: https://sharrowmarine.com/blogs/performance-reports/project-...

The issue, as far as I can deduce, is that the design of the prop needs to be almost perfectly tailored for the expected flow regime. Tweak the RPM, power, and velocity variables just a bit, and the hyper efficent, silent prop becomes detuned, negating any extra benefit it might have had. (In the link above, you can clearly see that the prop was designed for peak performance at around 2500 engine RPM). Contrast that to a typical prop, where you can get decent thrust and efficiency with just about any old scooped blade with a pitch angle.

Rctestflight on youtube gathered some fairly insightful, albeit limited data on this topic, would recommend! https://youtu.be/oXgp7IGnvKA