chrome lining is a non-issue. most will not have their rifles in jungle humidity or shoot corrosive ammo.
hk is billing the mr in mr556 as a mATCH rIFLE, dont know of many match rifle shooters concerned about a chrome lined barrel.
i only have one ar with a chrome lined barrel and that is only because aac makes their .300blk that way.
no nitriding? have not seen anyone say it is a issue. you can always get it done later.
spend less time paying attention to what spec it doesnt/does have, buy one and spend more time shooting.