In an AIO system, the heat from the CPU chip flows into the liquid inside the pump chamber clamped against the chip top. The pump circulates that heated liquid through a loop to the radiator and back. At the radiator heat from the liquid is transferred to air by the radiator, and the rad fans force cooler air though the rad fins to remove that heated air and exhaust it out of the case. Many system mount the rad and fans as air INTAKE units that use the coolest air source (the room air outside the case) and send that slight heated air inside the case where it can help to cooler more components on the mobo before it is exhausted. Note that the air heated by the rad is NOT hot - only a few degrees warmer than incoming cooler air.
I could not find a rating for max heat removal rate for that beQuiet AIO systems. I did find a review of a 280 mm version of the Pure Loop product. It says its performance is comparable to most systems of that type, although at the very highest workloads and heat outputs (200 to 250 W) is removes a bit less heat than some competitors. Your CPU is rated at 150W heat generation at low loads, and up to 240 W max heat output. So if you are running at its full workload capability, this cooler system will do the job but some others might be slightly better. For less intense applications you would not have any concerns at all.
80C is hot, bit not uncommon for a high-performance CPU at heavy workload. This CPU is entirely OK running that way. Its specs say its max junction temperature is 100C, so I expect it would actually try to slow down to protect itself somewhere over 90 C.