So. That means getting to the root of exactly why you feel you should buy liquid cooling over air. Me personally, I'll always choose liquid cooling if given the option, I much prefer the looks and openness of the motherboard, lack of covering up rgb ram, no restrictions on what ram, the fact aios come with extra fans I don't have to buy, most aios even have tailorable software for fan speed controls so I don't have to rely on the basic bios functions. But thats MY preference, I'll spend more to get what I want.
What you buy is more important than whatever you buy. Buy a good performance aio will be better than a miserable performance aircooler or vice versa. I'd not purchase a cheaper 'lite' version at half the price of an older nzxt Kraken X61 for instance.
So, why liquid?
The p400s can fit upto a 360mm or 280mm aio on front, so cooling potential isn't limited by size. Airflow is not so much a major factor for the pc on general, the gpu is the only component with any concerns. A difference between aircooling and liquid cooling, aircooling needs air Flow because the cpu cooler/gpu relies on case ambient air for cooling, a front mounted liquid cooler does not.