(Disclaimer: I work for Stratasys. Not representing company positions, etc.)
The PLA plus metal powder filaments are dense and hefty, but they don't have anything near the mechanical properties of real metal. "Sorta mostly metal" is a world apart from all-metal crystalline structure. PLA in general has crappy mechanical properties, though it does burn out nicely if you want to do some lost wax casting. If you need glorious metal off a 3D printer, what you really want to be doing is one of the following:
-Print a mold and then cast it
-Get a service bureau like Shapeways or SDM to make it on a big boy DMLS machine
-Wait a few years for next-gen "green part sintering" metal systems that Desktop Metal, etc. are working on
edit: Forgot the obvious choice, just CNC the thing. Aside from shops or making friends with a machinist, desktop CNCs have gotten much better in recent years too--they simply lack the marketing push that 3D printing currently enjoys. Better know what you're doing, of course, but none of these prototyping systems are "plug and play" especially on the low end.