Zero-Clearance Questions

I’m considering low-end ZC units given my likely usage in the Deep South (and my pocketbook), FMI ‘Craftsman’ C42L and Lennox HC-42 are two that can have blowers, air supply kits and doors added. Do the doors/blowers/vents available on these really help efficiency or are these fireplaces just for looks? I understand the necessity of using the manufacturer specified chimney system but are some brands best avoided to not get gouged by the manufacturer’s proprietary product pricing? What are the pitfalls of buying Ebay, Craigslist or closeout items, are there ‘orphans’ out there, accesories/vent-systems that are out of production or rep/installer-only-sales of components?

Sorry if I’ve asked things that have been asked before, I’ve searched quite a bit but still have questions, thanks for your help!