They are very good.

 

Chrome is important if your going to be using cheap steel cased ammo. It aids in extraction. A good portion of guns having issues with steel are ones lacking chromed chambers.

 

An M&P 15 uses a Melonite or Nitrided barrel which many say is more accurate than chrome. I have barrels with chrome, without chrome, stainless, phosphate and nitride treatments. For fun shooting I cannot tell any difference, for match target shooting I would do a lot of research with SS, chrome and nitride to find what suits you best.

 

A chromed bore was a must for shooting corrosive ammo. In modern rifles no big deal. I have read that chrome "slightly" reduces the accuracy, but considering the military prototype rifles, it is almost certainly nothing.

 

How are you gonna shoot this gun? Is it gonna be in training drills or such that requires a person to shoot 500 or more rounds a day? Is it a safe queen that only comes out a few times a year shooting with hunting. With that, is there gonna be mag dumps each time you bring the rifle out and have fun w/the boys?

A chrome lined barrel gives easier cleaning, rust preventative, protection to that barrel's landings/grooves(chrome is harder than the barrel's steel), easier round extraction w/chromed chamber for many rounds that shoot dirtier.

Someone with non-chromed type treatments will need to answer your question about durability and, or, if it can break down if you decide to do mag dumps or such.

 

Anything is possible

From just shooting a few magazines a week on my farm - to carrying in southwest TX in a gun truck hunting quail to being a a scabard on my walking horse in southern Arizona working dogs

To sitting around in the house not doing much - to fighting off whoever and whatever comes my way if anarchy comes

Not worried about cleaning necessarily - I shoot flintlocks all the time - so I can clean a barrel

 

Well, if shooting a few magazines a week on the farm is one of your intents, I would certainly get a chrome lined barrel.

 

It's important only if you shoot thousand of rounds a year or if you shoot corrosive ammo. But the corrosive ammo problem is not a problem if you clean you rifle after each session. I find my non chromed barrels slightly more accurate than the chromed ones.I wouldn't let the lack of a chromed barrel keep me from getting a rifle I wanted.