Rock solid - Daniel Defense MFR XS Rail Systems

I bought the 15" DD MFR rail for a 16" barrel. A note, DD has dropped the "XS" from this rail system. It now just says MFR but it is the same system. I found this to be extremely expensive for a rail. But I wanted it for its superior mounting system and the M-LOK attachment style. I was not disappointed in the quality. Everything you need to install this rail system is here including the barrel nut wrench, even some loctite 242.
Would I buy it again, yes. There is not one thing that I have found that I don't like. DD states that this will bolt up to any mil-spec upper receiver. It worked fine with mine, a non-DD receiver.
A side note, make sure you have your dust cover installed prior to installing this rail. I took it off to fit in my vise fixture and installed the rail. I had to remove everything to get the dust cover pin into the upper receiver and then reinstall the rail.
The included QD attachment device (shim) is needed (as I found out) because if you try to put your QD sling plug into the hole in the rail next to the receiver, it will bottom out against the barrel before it locks into position. This adds some thickness to allow you to use that mounting hole and moves the bottom of the QD plug away (outward) from the barrel. This was obviously thoroughly thought out.