As to muzzle protection while loading, I have never used it. My .69 shows a small groove in one rifling groove at teh muzzle which might have been caused by rod wear when examined closely. This tiny groove does not seem to hurt it's shooting capabilities in the slightest. This is probably due to the big ball and large powder charge it uses. Smaller bore sizes would be more susceptable to any damage effecting them. I do not know how many shots it's fired, but perhaps 5 or 6 thousand and a nylon rod was used for loading, perhaps 200 of them. All the rest were with a hickory rod, the one that's still in it's pipes.
I'm of the opinon that a rod that is quite large diameter in the bore, will cause less damage than a small one, due to begin less liekly to flex and rub the bore down inside. That type of damage is what happens to many modern rifle barrels, with the tiny diameter rods used. The rod flexes due to tight cleaning patches or when loading. Most modern rifles are damaged when cleaning. I suspect the same thing happens with muzzleloading rifles IF a steel or fiberglass cleaning rod is used. The bowing inside the barrel, rubs the edges of the lands. This type of damage was recorded when steel rods were used in the round ball and minnie firing military rifles. se; "Firearms of the American West 1805-1865". No mention of damage from hickory rods was made.
In my less than scientific experiment, a hickory rod wore the metal less than any other material, which included brass, stainless steel, tool steel, nylon and fiberglass. The hickory rod barely wore off the bluing with the nylon wearing off more blueing, but not removing steel. All the others made measureable grooves,w ith the fiberglass rod making a deep groove similar to a fine rat tailed file. It was non-protected fiberglass - raw, which would happen when a protective coating wore off one of the comerical rods.