The style of backband you need really depends on what type of vehicle you have. If you have a two wheeled vehicle or four wheeled vehicle with fixed shafts (ie. when you lift one shaft they both rise, they are fixed together and move together) you must use a sliding backband. This is because as you travel over uneven ground or camber, the vehicle will alter its angle which in turn makes one shaft higher than the other. The sliding backband allows the tugs on the backband to move up and down with the shafts. If it didn’t do this you would be putting pressure to one side of the saddle which would be uncomfortable or may cause the saddle to slip.
Driving saddle with sliding backband
If you have independent shafts (ie. you can lift one and the other remains on the ground, they can move independently of each other) then you need a fixed backband. As, in the scenario above, the shafts can move allowing for uneven ground or camber. If the backband were a sliding one then you would end up with one shaft up and the other down as it would never correct itself.
Driving saddle with fixed backband
You can fix a sliding backband using removable conway buckles if you had two different vehicles for instance, so this is the most flexible option.
Conway buckles in use on a sliding backband driving saddle