Originally Posted by Mr. G36!
Surely the ability to clip them together without needing a clamp is worth something?
I have to agree with LUNIT on that one, whatever the clipability is worth is far outweighed by the inconvenience. Piecemeal you can only fit one in a standard double mag pouch (unless you're using specific G36 mag pouches), and clamped together you'd need a huge pouch just to fit two.
As for the practicality, whatever speed gained for reloading one mag just isn't worth it for me. I personally find the AR's free dropping release to be quicker and more efficient than having to rock mags in and out, and coupled with magpuls (homemade or commercial) and a dump pouch, it's just as quick, except it's that quick for every mag you've got.
On the G36, clamped mags also interfere with the ability to fold the stock (not a major issue, but annoying when you try doing it and it bumps against your mag).