Odyssey's new Ballistic Pack system has the tensioning system built into the pack, not the belt, greatly improving comfort.
It incorporates features designed by the medical industry.
Ultra lightweight, super comfortable, lumbar support and it is vented to breath.
Belts are available small through extra large.
Packs are available as a 2+2, 3+3, 4+4, with more coming.
The Odyssey 2+1 Pack is older, so while it may be available used and in a few cases new, it is not commonly available anymore.