If the low number of ratios, wide RPM drop and low torque multiplication are acceptable compromises, the PG offers a big advantage: wouldn't it be nice to delete the entire "clutch question" (weight, spares, throwout bearing, inertia, linkage, leverage ratio, room in the cockpit for the control, less things for the driver to think about)?
I never thought I would say this back when I was young, stupid and completely broke (now I'm old, senile and almost poor) but any problem I can solve by buying something commercial (viz., known quality product, spares available by FedEx, does what I want) rather than make another fabrication project out of it... I'll just pay for it.
There's always something else I can't buy that needs my time and energy.