Slant 6 Distributor

I have a couple questions. If I replace my distributor on my slant 6, do I want it to have a nylon or metal style gear, and what is the advantage or disadvantage. Also, is this control box on ebay hype or something I should consider? And, would this part allow me to make future performance upgrades without having to do it a second time?

MOPAR Hi-Perf ECU Electronic Ignition Control Module Upgrade Dodge Plymouth | eBay