I have a pulse counter and I've used it to show pulse output on EKM Metering's 3/4" water meters, which BTW are low cost at $70. I believe you should be able to use their 2-wire pulse-output water meters for irrigation systems.
For example, I used Monnit (1-input) 2-wire pulse counters and their ethernet gateways to push my water flow data to the iMonnit cloud server. I even rigged up an Arduino Uno and a hall-effect (3-wire) flow sensor to do the same thing, using Monnit's pulse counter/transmitter and ethernet gateway. The Monnit (4-input) 2-wire pulse counter seems to be a little better, as I suspect but not sure that "pulse lockup" issues may be affecting the 1-input memory registers.
EKM had some similar issues on their earlier v.4 systems whereby the pulse counts would stop if the v.4 meter saw anomalies on the voltage inputs. A power cycle cured that issue.
Recently I just dropped $200 into a Hunter 1in. Flow-Sync and saddle-body tee. A 2-wire system, so I thought it would be plug n' play. It appears to be proprietary for their I-Core controllers. The drawback is that no flow data gets pushed to the cloud, the data stays in the controller so all the smart decision-making wrt water flow is internal to that device only. Bummer, no SMS text alerts or cloud graphs of flow to check up on! I am guessing that, since Hunter controllers supply 20vdc to the flow sensor terminals to function adequately, that it would be necessary to 'energize' the sensor with a little bit of DC to get a pulse counter to test output. If you hook up a pulse counter to 2-wire (red/black wires) from the Hunter Flow-Sync, there is no measurable output. So I'm thinking it needs some voltage to get the signal, similar to 3-wire hall-effect flow sensors(signal, positive and negative) which only need a 3.3vdc supply to push out the pulses to measure.
So could Rachio update their system to supply 20vcd to Hunter Flow-Syncs? I'm thinking that would solve the compatibility issues.