If your gate post is not installed properly so that the gate moves with the soil, then I can definitely see the 2 way latches being a problem.
I’ve not ever had that problem because we (my husband) is anal about the gate posts being rock solid - deep in the ground - braced out the wazoo so they don’t shift.
The 2 ways DO prevent gate sag on gates that stay closed most of the time, as they do support the end opposite the hinges. When I have a long gate that is open often, I support the end with either a wheel or one of these: http://www.speeco.com/products.aspx?id=8&prod=17 . The anchors prevent the gate from freely swinging when they are “set” but they can be raised and locked in an “up” position so the gate will freely swing.
Also, I never, ever, ever, ever let ANYONE, no matter their size, climb, stand, or lean on my gates. Doing those things is asking the gate to sag.