Frankly, I don’t have too much use for it on an AR.
Seems to me that wiping down a bolt carrier with it is going to get the cloth pretty dirty unless the carrier has already been scrupulously cleaned.
However, upon application, the fluid from the cloth dries out in a minute or so, so it might be good for extreme low temperatures and/or sandy conditions. Otherwise, I’d rather just use CLP.
It does give a nice, dry, really good-looking finish to the outside of the AR receiver.
Magazines are a different story. I very much like using this on steel handgun magazines, primarily for rust protection.
While aluminum USGI magazines don’t need this, it actually might be worthwhile in minimizing wear as magazines are inserted and removed from an AR. It doesn’t appear that the fluid will remove the powder coating from these magazines.
This cloth appears excellent for knives and other things – like tools – that might rust.