In reply to Tall Oak:
I have a metolius on my back and an ocun moonwalk that attaches to it just using the provided strap, no need for a ratchet thing or a dedicated strap. The pad that goes over the back needs to have a strap that you can put in shoulder carry mode rather than rucksack mode, so that it will wrap over the pad you are carrying - pads with only fixed rucksack straps are no good.
I have a couple of smaller (<5kg) ones that I carry in my hands. Two is much more effort than one on a long walk in as with only one you can swap arms regularly. It's not really a problem at all.
I have also put my old large pod pad (normally unused now) over the top of the metolius as well so that I had three on my back and one in each arm, to pad out Art of White Hat. Unfortunately I was so knackered by the time I got there I could hardly climb, that method is not recommended
I've been using the metolius like this for 5 years now and it's still going strong.
Post edited at 20:47