So I'm about to order an Adams Arms piston setup for a 7.5. AR pistol

Is it worth it to upgrade to the NIB Carrier? It's only $9 more.

I know piston setups don't really need that coating since they don't run as dirty. I'm wondering if the NIB or standard Melonite finish would be better long term.

Any input would be appreciated.

As you said the carrier stays clean but for $9 why not, just makes it easier to clean.  Make sure to get a good bolt.  I went with WMD NiB for $60.

I would go with the melonite.  I have 2 AA uppers that each came with AA's melonite carriers.  I also have a NiB carrier for my 300 BLK upper and it is stained to hell and discolored already (about 200+ rounds).  The Melonite carriers won't show the dirt / staining / discoloration and I've find that they wipe down every bit as easily as the NiB carrier.  I won't do NiB again, from now on it will be melonite for me.

FYI  I had the same problem with my NiB and found it was the lube that was staining it nasty colors.  Also do not use Hopp's on them as it will stain them also.  They cleaned up nicely with Flitz metal conditioner and I changed lube (Mobile) and they never stained again, look brand new after 1000's of rounds.

NiB has a little more lubricity than Meloinite.  Melonite is black.  NiB is a coating and Melonite is a bonding.  Your really down to a personal preference on color as their both very nice.

Yes, I know.  I run M-Pro 7 lube and as far as I know, it's not supposed to be an issue.  Regardless, I prefer melonite having now used both types of carriers.

This... melonite is IN the steel, NiB is ON it.  Drop your melonited BCG and no biggie, but you run the risk of chipping NiB as it is a coating.  Both are hard, both are non-stick.  Being a piston gun the only reason I see to go NiB is if you want the "bling" factor.

Or..... You're like me and run it dry.