Yes, I would also assume PSI also
For the 1/2" low flow units, the pressure drop for 3 GPM (180GPH) rate is very low (ie almost zero)
Most of us are lucky to get more that 90 GPH (1.5GPM) flow thru our systems.
But I see now that they only go down to 1.5GPM. Oh well, you guys with higher flow rates might want to look at this