Man arrested for 2x4 labeled "High Powered Rifle"
These weapons are not identical for what purposes they can serve. Here are some differences that make a difference in a combat scenario.
Those two rifles are not equal. One has a collapsable stock, which also means it can be changed out. That means it can be concealed easier because the total length of the rifle can be shortened, as well as making making it easier to pan around corners or maneuver with the weapon in a ready position. It also has multiple rail mount systems (one on top, one on bottom). This has a potential to make you more accurate in firing in multiple scenarios because you can slap on anything from NVG sights (night vision) and lasers to a high powered scope or a blinding flashlight. Get a marking pen and sight in a few different tools that go on those rails and you can go from desert warrior to urban night sniper in a matter of seconds by marking where you sighted in your tools on the railing.
I also guarantee the second weapon will take a lot more of a beating then the first which is something required for a weapon planned to be used in an assault. The second rifle also has a grip handle, making going to the ready a lot easier and efficient then the first which will require a lot more skill to be standing straight up and "combat gliding" (walking at the ready) towards a target or in the direction of the target. You also have the option on the second rifle to change out the pistol grip and stock giving you even more options to make you quicker and more accurate. The second rifle would also be easier to conceal due to its collapsable stock.
I can't really tell if an extended mag for the second rifle would work for the first, but generally speaking assault rifles have magazines from 10 - 30 from what I've seen, the first doesn't appear to have that.
Without stating my own beliefs on the gun control issue I can tell you I can do a lot more damage with the second rifle then the first, and that they are not created equal. The second can serve well in both an urban and rural environment, and although the first can be used in both it is not as efficient in design as the second for both situations.
Edit: Another option you have on the second that is not on the first, due to the muzzle compensator on the second, is the option of having a silencer or suppressor attached to the muzzle. On top of making the rifle easier to conceal, with those tools you can make your position easier to conceal as well because people can't locate where your'e shooting from as easily, if they can at all.