Note that both the links you posted are for the racks only - which mount to the bike rear rack and let you mount that specific vendor's top-case (at additional charge).
Don't go cheap-o, but you don't need to spend top-dollar (or top-Euro) to get a functional case.
That's a decision only you can make because top-cases are built to meet certain needs. For some it's camping and touring, others commuting, others going to school, some it's groceries, etc.
What purpose do you want to meet?
These forums are a great way to get feedback on one or another case. Both the racks you linked are for good equipment.