"So, if I take my time and weight map my M3, V3 and F3 (assuming I buy him), I can expect results in the ballpark of what you got with David?"

I don't see a reason why not.

I started by just converting the default rigging, so I could concentrate on fixing and refining the shape.

Weightmapping is tedious, but once you understand what the settings do, easier than the old rigging method.

Base M3 and V3 used to be free, while David and SP3 bases never were. So I guess them being more expensive now is just a "legacy" thing to not annoy the customers who bought them when V3 and M3 were free.