Tom, there is nothing wrong with such a flow meter, they will be highly accurate if properly calibrated. But I think it is overkill. A properly maintained modern municipal water supply is pressurized using large pumps (at least here in the Netherlands) and should deliver fairly constant results, although I realize there may be demand peaks influencing flow rate...
A normal tap has a metal thread that should give pretty consistent results if you count the number or "turns"... just try it out and see how repeatable it is over the course of a day. You can always go the "high-tech"

option afterwards...