I presume their meter is based on the TDC-GP30-F01 Ultrasonic Flow Converter sensor.
There is some background on that in elekor magazine. Not sure how much DIY you want to do, but there are development boards for this sensor available.
It is indeed a sensor that can recognize pipe flow patterns, so one would be enough to recognize (hopefully) the washingmachine from the toilet.
Ultramis and Kamstrup and some others make ultrasonic watermeters, but I am not sure if those can be used without cloud. The KAMSTRUP flowIQ2102 transmits data via a radiotransmitter and stores 480 days of data that can be read through an optical port, but as you are asking the question on OpenHab I guess you prefer something that has WiFi connectivity, but if you ‘just want a clamp on meter’ maybe the DCT1438K Ultrasonic clamp-on flow meter is something for you
Mind you that those meters generally are not cheap. The Fluid will eventually retail for 300 USD and that is not out of line with what I have seen on other ultrasonic meters. The DCT1438K is around 150 I think