I’ve mostly used SOLGW nitrided BCG’s with zero issues. Recently I decided to try a coated bolt carrier just for shits n’ grins. Bought a Sionics NP3-coated. I’ve owned a lot of NP3 coated firearms and firearms parts over the years and have been very pleased with it.
My carbine was 100% reliable before I swapped the BCG out for a coated one; it’s still just as reliable. When I cycle the bolt by hand, it feels smoother. So far, biggest plus for me has been how much easier it is to clean over the nitrided bolt.