All of Wilson's Bullet Proof line are machined from solid bar stock as opposed to MIM (Metal Injected Molding). Same for Ed Brown's Hardcore parts. Note that it's not extended though, the BP slide stop is pretty skinny. The difference in the machined vs. MIM shows in that the BP part is nearly double that of the MIM part.
When I build a carry gun I always use bar stock parts from Wilson, Brown, and Caspian. Some of my plinking guns or even one of my Single Stack raceguns use a few MIM parts; the Wilson extended slide stop being one of them. Hope this info helps.