While they are probably the best of the mag couplers, I have found that all mag couplers suffer from a couple of serious problems that have led them to be rejected by virtually every military and most police units.

The most serious problem of coupled mags is that the ammo in the "spare" mag tends to walk forward under recoil, which will prevent you from seating the "spare" mag when the time comes and can jam up the gun.  Other problems include the ability of dirt and debris to get into the open "spare" mag, and the possibility of the feed lips to get hit on something and bent.  Finally, how do you store the coupled mags?  Do you drop them when they're empty, or do you have some kind of pouch to hold them?

Anyway, I recommend to everyone that you should instead invest in some good mag pouches and practice mag changes.  That way, you'll be doing the same thing EVERY TIME, whether it's your first mag change or your fifth, so your muscle memory won't be confused, and your mags will remain protected and clean at all times.

It may not be "Hollywood sexy", but the things that work best rarely are.

-Troy