No, the flow meter was never actively used by the firmware on older machines. It was originally installed inside the machine under the assumption that it would eventually be useful, at the very least for calibration purposes. When the component was permanently removed from production, the only firmware adjustment required was a minor update to the physics model to reflect that the physical resistance caused by the meter was gone.
Aside from simplifying the machine's internal design, removing the flow meter actually gave the espresso machine a slightly higher overall flow rate. Although the part itself was inexpensive—costing less than three US dollars—removing it eliminated the friction it naturally introduced to the water line.
Transitioning to an open-loop system where flow is predicted rather than mechanically measured took four years of internal debate. However, the debate ultimately ended because mechanical flow meters in this category are highly inaccurate, suffering from a variance of plus or minus 15% (a 30% total range). In contrast, Decent's developed physics model is far more reliable, maintaining a strict accuracy range within two to three percent.
While incredibly accurate mechanical flow meters do exist on the market, they are not feasible for an espresso machine because they are physically massive and cost thousands of dollars. Furthermore, they are simply not fast enough to support Decent's rapid water-mixing technology. To mix hot and cold water instantly, you would need highly responsive meters on both lines; ultimately, no mechanical sensor responds as rapidly as the physics engine counting the raw strokes of the pump.