The reason for barrel coating is to makes it last longer, faster, and more accurate. I don't see any disadvantages of any coatings. Otherwise, why would any one do it? There are number of types of barrel coatings which you can simply google for them. Anyhow, don't worry about coatings. Well known reputable brand will do great job on their barrels and other not so much will be little lesser of quality. You will get what you paid for.