The DPMS and S&W can get the job done. Doubling the expense on a firearm that may never be used in urban combat is an individual choice; and apparently there are plenty of individuals who are choosing to worry about it. Since most of them are also going to the same ranges, shooting the same targets, and using the same ammo, it's a lot about establishing a social pecking order so you will know to genuflect appropriately when their shadow falls on you.
IF - IF - IF you plan on getting into any real hard use duty of a gun, the appropriate authorities supervising you will supply it. Even LEO's are being issued older M16's for their trunk guns. What that has to do with the civilian purchaser means nothing, not even cops get to practice enough, and certainly not thousands of rounds a month. It's mostly a dedicated HSLD player justifying their expenses with doomsday scenario thinking.
They usually miss the fact you can't carry an AR15 concealed, said pistol would be your first line of defense anyway, even at home. And, the statistics prove that, most intrusions are settled with less than three round fired IF a handgun is discharged.
The guns mentioned will do fine - they are mostly clones of the military contract M16 or M4. The specific parts not automatic are deleted, no problem there. Their quality control and durability are going to be less than military grade, you get what you pay for. Some detail like, a Magnetic Particle Inspected bolt might not be done - individually inspected. That costs money, and the .Gov does it to catch a few before they could fail early. After 5,000 rounds of use, they ALL need reinspection. A civilian shooter might take ten years to make that benchmark. A military issued gun, 6 months. It's a matter of perspective and use.
Don't expect a target trigger, or even one as good as the cheaper guns on the rack. That can get upgraded easily enough, Amy Giselle is selling a new manufacture drop in military grade trigger that's everything a soldier would really need. But, it would still be 4-6 pounds pull, with some creep - precisely because a military trigger is made with rough use in mind, not range or benchrest shooting. It keeps soldiers from shooting each other in the back, a worthwhile accomplishment.
What you will enjoy with the AR15 is cheap ammo, easy take down to clean it, if you want to bother, robust construction, and a lot of anti corrosion treatment to keep it functional. It is not "pretty" like the rest of the guns on the rack, because it doesn't have polished steel that requires a lot of maintenance to keep oiled, highly finished wood that cracks, dents, and swells when wet, or parts you can only get from the manufacturer. AR's have become a widely sourced universal platform, and given a few don'ts or incompatibilities, most parts swap literally from gun to gun to gun. The blueprint specs and makers hold so closely gunsmithing is nearly unneeded - even barrel swaps. It's held on with a nut trapped by the gas tube, lots of guys literally assemble them on the kitchen table.
That means if you want to make it a CQB special with NRA taxed short barrel, or a NM competitive rifle capable of making the standings at Camp Perry, it can happen, and all work done by the owner.
Buy the rollmark of your choice, the expensive ones charge more, but like Rolexes, you get your money back. And like Rolexes, you might pay more, but it still just puts a bullet down range. What people argue is the amount of needed accuracy and how much durability it might need - which is something the individual has to specify for themself.
Obviously, not everyone wears a Rolex, and not everyone shoots a $1500 boutique rifle, either.
