Can you explain to me, what is the point of these?

To make money off of "tacticool" people that want the weight of 2 full mags hanging off their AR.

2 full mags, plus 2 weighted mag extensions.

Makes it better for butt-stroking.

I like mag couplers. I store my Go to rifle with an empty mag locked in and loaded mag free. If I need it I just pop in the loaded mag. The gun was never loaded but close to it. I like the way the mags are staggered. Even side by side I do not like as much.

So somebody breaks into your house...

You have to fiddle around in the dark and find the mag release button, drop the empty mag, transition to the loaded mag, insert it, pull the charging handle, and then you finally have a loaded weapon

The Magpul Couplers look to be more sturdy, as they connect toward the middle and allows for some adjustments.

Friend, I say this out of concern-  but you're doing it wrong.  At the very least, keep a loaded mag sitting on a closed bolt.  At least this way you only have to charge the weapon to make it ready.

+1 At the very least.

This is exactly how I store my one and only rifle.  I totally understand what the other comments are saying about having to take 3-4 different actions prior to being able to use the rifle in an emergency, but having young kids in the house (two girls), I can't sleep well knowing there is a loaded mag in the gun.  I know my kids, and they cannot and will not be able to eject a mag, load a fresh one (that they can't even reach), pull the charging handle back (they don't know to do this, and can't even physically do it), and even hold up the rifle itself (too heavy for their weak girly arms).  That is why my AR is NOT my main go-to self defense gun.  My CZ SP-01 Tactical is, and it's in a locked safe on my nightstand.  The rifle is just there in case I for some reason cannot get to the pistol, and have to retreat to the closet where it is stashed.  None of this is ideal, but you have to do things with kids in the house.

Better to be safe than sorry, you're doing the right thing.  I have a theory about security: you have to know your physical security to develop a defensive or offensive plan.  I harden my doors and windows so I have time to chamber a round from the time I hear the door or window being breeched and make ready.  It's relatively inexpensive to harden your home with a little elbow grease.  I always leave a loaded magazine in, and you should too unless your children are in question.  I have trained my children in the fundamentals of gun safety and handling.  Obviously at a very young age this is impossible but they are physically unable to chamber a round so this is an added layer of safety. Keep it out of reach and the children educated is critical.  When you have guests over you really have to maintain control and lock up stuff 100% of the time.  When the kids get old enough to get into things keeping everything locked up is more critical.  And education is more critical.  My children are so well trained I have no safety concerns.  We routinely discuss gun safety fundamentals and get plenty of handling time in.    So with proper training and education a family can be very safe around guns.  It requires a good deal of training and time invested but it's worth having the peace of mind that your children will never shoot themselves or others accidentally.   Buy a dummy gun and have them practice the proper ways the handle it.  And let them know never to handle it unless you ask them and are present.  Kids are extremely loyal when given responsibility and trust.  At the same time secure your guns so it's a non issue.  Some kids do have learning barriers, and deficiencies. Maintain 100% control over your defensive guns/weapons while in use.  Lock them up when not in use. When your kids are ready they will be able to defend themselves, but it requires lots of training, education, and range time.  If you fear the boogeyman in the middle of the night, you should harden your home so you don't have to be concerned with a 60 second response time.  Have a plan and set your home up so you have a few minutes to prepare to engage a threat.  Technology is cheap and readily available to harden and secure your home these days.  You can set up motion activated lights and cameras with alarms along with hardening your doors and windows to make it virtually impossible to break into your home without a great deal of forewarning.