U-tube is just a glorified pendulum. But using this classical U shape for liquids is worth it. Pendulums is how you measure mass if gravity is too low.
I know some people inverted U-tube and immersed piezo fork into liquid. Then they struggled with reflections and setting feedback right or making sweep practical enough. And then there is electrical connections going into the probe through liquid surface, which is another concern. Still, in batch process (and all brewing is batch process) immersible probe should be much faster and washable than flow-through, I guess.
Awesome, I should totally start making these things too and place them in my microcloning and brewing yeast webstore. This dude is a hero of our biopunk culture, weird that I haven't heard about this before!