Rear lights don't have the internal gubbins to regulate the power output from the dynamo so need to be connected in series from the front light. You cannot hook them straight up to the hub as this will damage the light. If you get the cheaper one then you will need to use a battery powered light out back.
On my touring bike my current approach is bright dynamo light up front and a battery powered rack mount cateye on the rear. This way I didn't need to faf with running rear cabling and I find the battery powered rear has enough life for what I need.
Rear lights don't have the internal gubbins to regulate the power output from the dynamo so need to be connected in series from the front light. You cannot hook them straight up to the hub as this will damage the light. If you get the cheaper one then you will need to use a battery powered light out back.