I have never used the Duracoat product line, but I have used the Brownell's and now the Norrell's. I had been using the Brownell's product for a few years for coating handguards after cutting the vent slots into them. I was always very meticulous in it's application, and was quite happy with the results. I don't think the Brownell' product was nearly as durable as the Norrell's that I'm now using, but it wasn't bad.
When I started building my integral compensator, I spoke with the technical staff at Brownell's and was told that their product would probably not hold up. I exchanged several emails with John Norrell and he seemed very confident that his product wouldn't have any problems with the temperature, or blast from my integral compensator.
I have a gunsmith friend from Iowa that has used the Duracoat, and was not at all happy with it's durability. He told me that he could often mark the surface with his thumb-nail. I have never tried Duracoat, so I can't vouch for his statement, but I do know the Norrell's moly-resin is VERY hard and durable.
The "flatness" of the finish is dictated by the temperature that you preheat the metal to. The higher the temperature that you preheat it, the flatter the finish. When I first got my oven done, and my Norrell's in-stock, I decided to coat my own .243 WSSM barrel. It was fluted and had my integral compensator. I didn't think about it while I was applying the Norrell's, but the hollow compensator didn't have the thermal mass that the main part of the barrel had. When I began spraying the barrel assembly, the compensator cooled quickly and received a glossier finish than the rest of the barrel. I made the mistake of baking and curing the barrel. The shiny compensator was very conspicuous! I decided to start over, so I took the compensator to the belt-sander and started to remove the Norrell's coating. WOW! That stuff is really on there! Black dust was flying, and I never did get down to the base-metal. I'm sure I could have, but I had the surface roughed up like I wanted, so I just stopped there.
When I went to re-coat my barrel, I would take it out of the oven, give the compensator the first quick sprays, then move on to the rest of the barrel. The theory being that the hollow compensator would not only cool quickly, it would also re-heat quickly. The theory worked out perfectly! I achieved a nice, homogeneous, flat-black surface on the entire barrel.
Once Norrell's is cured, it is impervious to bore-cleaners, salt water, acids and temperature to 1800 degrees F. It will scratch and wear, but then so does bluing or parkerizing. I have modified how I prepare my compensators and flutes for coating. I round all of the edges. Sharp edges are the first to get worn.
There is a very fine line between "hobby" and "mental illness."