Better temps & aesthetics. The blocks are all the same so the flow through each block is the same, there's also hardly any restriction in the loop so the pumps can be undervolted a fair amount.
We usually use D5s in this build, but we're trying to get the best out of the Aquaero this time, so we're using PWM DDC pumps with EK housings. Each rad will have it's own channel on the Aquaero, so will each pump. There will also be temperature sensors and flow meters in each loop for 100% monitoring and automatic control of the system.