yeap i ordered it from caseking today... It comes 25€ cheaper with DHL.The vantages of AIO would be more not blocking the RAM with a massive cooler (considering your case allows the installation of the radiator at an ideal location), and easier to install. That's all.
Custom loops allows upgrades, as cooling other components.
Regarding prices, the idea of the kit is that would offer better value than individual parts, as packaging would be reduced, and the manufacturer manages to "push" few bits at their price, without being noticed, as tubing and connectors.
Worthy checking at https://www.caseking.de/, if prices may work better for you.