In milder climate where it doesn't get extremely cold low tensile wire can absolutely be stretched tight enough where it doesn't loosen up. The major difference between the fixed not and hinge joint net wire is that the vertical stay is a solid piece of wire, not broken at every horizontal. That's what gives it it's stiffness and allows for wider post spacing. Stiffener post can be done without if tpost are put in deeper or into rock. A few more cents on buying 1.35 or heavier tpost compared to the farm store 1.25 goes a long way.
Pipe post outlive wood, don't burn, if you hang it going through the gate it bends and doesn't break. Turn around and bend it back. If it loosens it wasn't set deep enough. The absolute most important thing is depth. 3'-7' on brace post with 3' only being good enough if your rock drilling in solid rock.