The barrel description is here:
https://danieldefense.com/cold-hamme...hf-barrel.html
This is a fairly heavy weight barrel. The overall upper is going to be fairly heavy and balance pretty far towards the muzzle. It would not be a good 3-gun setup (unless you can bench press a Toyota). It would probably be an excellent semi-precision upper for use with a bipod or off a bench.
The barrel is a fairly new profile for DD, although S2W with midlength gas has been around for a while. The rail is somewhat older as you said. Whether quadrails are obsolete is a matter of opinion. But they are definitely bulkier and heavier.
All Daniel Defense factory-assembled uppers are top quality and made the same way. Western's description clearly says this is a DD factory-assembled upper. No worries about quality or skimping. However, it is an older handguard as mentioned.
The barrel is nitride treated, rather than chrome lined or bare steel. It will last a very long time in any semiauto use. Accuracy potential should be good, but since they use a 5.56 NATO chamber, it may not be as accurate as a premium precision barrel with a match type chamber. You probably won't notice a difference unless you are a skilled handloader or use only match quality ammunition (like Federal Gold Medal).

