Not sure,other than the finish? Did you hit both during the fitting? If so, did you see a difference? If not, then it may not be worth the extra $.

Chrome was not tried during fitting but have done a little more digging. Turns out they are significantly different shafts, hence the upgrade cost. Comparison image attached.

I don't know what clubs you are ordering, but on the Golf Galaxy website if you select the custom option for Titleist irons when selecting the NS Pro 880 AMC (not the 880 AMC Chrome) there is no uncharge shown. Seems like it might be worth investigating.

Has anyone gotten to the bottom of this? I am wondering I have the chrome or the regular. Was told they were the “uncharged” shaft but they don’t seem to have that “Smokey” finish.

I have a set of AP3 with the NS Pro 880 with the gray clear coating. I was told the only difference was the gray coating finish when I ordered them. These are the shafts that were in the old Concept irons (C16?). I ordered the chrome, but they were backordered for so long that I asked about the gray finish. They were in stock so I got those. I am glad I did, because they really look good. They look very different from the chrome. So different I am sure from a distance people think I am playing graphite shafts.

I picked up a C16 wedge recently, that has the NS pro 850gh.
I saw a vokey in a preowned inventory with a NS pro 880 amc, and thought they were the same until I looked up the specs.

I'm still wondering if they play similarly. 880amc may have replaced the 850gh or could be completely different.