Honestly, you don't need either IMHO. I used to tape mags together myself (one upside down) and discovered that I either had to be very conscious of what I was doing or I ended up with one mag full of dirt and crap, or found the feed-lips damaged. I have a lot of friends who put multiple mags on their weapons and all it does is add weight and bulk to the weapon as well as sticking a mag out to catch on stuff and get damaged. After years of experiments and trying to find a solution I came upon a simple answer, just don't do it.
First, I have 20 to 30 rounds in the weapon, and if that ain't enough then I needed to get the heck out or get my full LBE with it's butt-load of ammo.
Second, I discovered that I was generally as fast getting a mag out of my hip-pocket and reloading as my buddies were using their redi-mags or jungle-clips or whatever simply because these devices have their own learning curve, yanking a mag out of your pocket and reloading does not, it is no different than reloading from a pouch.
lastly, I discovered that the change in weight and balance of the weapon with an extra mag attached by whatever method made a significant difference in how I handled the weapon, which might impair my operation of it in CQB situations. Given that I have generally used main battle rifles like the M-1A, FN and CETME this is especially true.
I would also mention that the availability of more rounds might (I say might, it depends on your training) effect how you shoot, I've noticed before that having more rounds available tends to make people pay less attention to accuracy than those who know they have limited number of shots. I think the difference in police shootings between when they had revolvers and after they switch to hi-cap semiautos bears this out.
Again, my advice is forget the gadgets and concentrate on good training and weapons handling skills.