For all the HVAC experts! 2 level difference
Residential zoning has come a long way, but like anything else dealing with a complex mechanical system, it must be installed properly. I too have seen some butchered zoning jobs, but with proper installation (the bypass should NOT just jump the supply and return, for example) and setup, a zoning system can be a great addition to a multizone structure.
I'm not sure what you mean by the "economy" of the system, but in general a properly zoned system will be as economical as any other, and in fact will often be more economical overall, since the homeowner can often avoid the cost of a second system.