You can't skip on accuracy
The front rail has a unusual extruded shape that pulls the fence square when the camlock lever locks it into place. The fence arm itself measures 60mm high and 430mm from the clamping arm, so it should reach across the distance of most tables.
The rear rail is there to support the back ledge of the fence arm, so table width is not critical. The viewing lens on the fence arm itself is magnified, which makes it easier to line the fence accurately against the graduations.
Which fence should I choose?
After careful adjustment to get the measurements reading accurately, clamp the fence arm to the front rail and then lay the whole assembly on to the bandsaw table to exact where to drill the holes.
The great news is that the holes on the front rail are elongated so once you have the fence basically correct, you can fine tune it by loosening the bolts and sliding the fence along the holes until it lines up superbly. This is a fantastic way of ensuring excellent accuracy in your cuts.
Note: The elongated mounting holes are set perpendicular, not parallel as pictured.