"Normal" soft saddlebags are attached to the bike by draping a wide strip of leather (the yoke) that's stitched to each bag across the rear fender, either above or (more usually) below the pillion seat. There's brackets mounted to the sides of the bike that sit behind the bags to stop them swinging into the rear wheel. The bags're usually tied to the bracket with laces and're considered a temporary fixture - easilly removed. As far as I know the Triumph bags are this sort, where the yoke cannot be removed from the bags without cutting it off. In contrast "normal" hard bags (made of fibreglass, plastic etc) are bolted to either side of the rear fender and are considered a "permanant" fixture.
This system has two downsides; to be fairly secure the yoke should be mounted below the pillion seat, however as the bags move around a bit when the bike's in motion the yoke rubs on the fender which can cause fine scratches in the finish. It also means the bags are either insecure (on top of the pillion seat) or hard to remove (below the pillion seat).
Brackets like ghost brackets and easy brackets (and the ones on the KDrive bags) are designed to have soft bags bolted to a steel plate, which is then mounted on studs/rails that're bolted to the bike, and locked in place by some sort of key & lock. This means the yoke can be removed/omitted from the bags. Some bags have a "removable" yoke that's attached to the bag by some form of clip, either so that the bags can be detached from the yoke and carried about like small suitcases for security, or so they can be used with ghost/easy brackets etc. This requires that you buy bags with a removable yoke, and that you drill holes in the bags and mount the plates yourself. It also means that the weight of the bags is hung from positions the bag manufacturer never intended, and we've had members whose bags have ripped from the mounts.
The beauty of the KDrive system (as I see it) is that the bags were designed from the start to be used with their brackets. There's no chance of incorrect mounting with misplaced holes, and the weight's hung from where the manufacturer intended. The only design issue I've heard with these bags is that the keylock is access from inside the bag which may make it difficult to access if the bag's completely full.
Oh and far as the leather vs iparex issue goes, most soft bags are some sort of synthetic leather so you don't have to oil them weekly, keep them dry in the rain etc. The only real advantage to genuine leather is the "brag factor" which'll soon go if you fail to care for them and they start looking like old worn out shoes.
Matt
