Wonder who that mysterious initial partner is
That being said, I would advise against buying one with expectation of compatibility with Rachio. Pretty sure there is some sort of serial / firmware based authentication that is going on. Within the app, I see Specific serial number and firmware version “flow-ota-combined-53”.
Body / housing may be the same, but does not mean it will work out of the box. Alas I do not know if Rachio has any plans to open up response conditions (such as zone shutoff on a high flow) for a hard wired flow sensors, as far as I know any other flow meter is used for a zone consumption measurement only.