It is true that the AL monitor requires several calibration loads, and the Deere system only requires one. This is because the AL flow curve is non linear, and the Deere curve is linear. When you calibrate at a given flow rate, Deere takes that flow data and makes projections about where your values will need to be at higher and lower flow rates. In their non-linear system, AL requires cal loads at low, medium, and high flow rates. This provides greater accuracy over a linear system, although it does require more work up front.
New Holland also uses a sensor with a linear curve. Case IH borrows from AL, so their sensor is non-linear.
Not sure what Agco uses...