rs1800
DS-7608NI-K1(B) - there is no cooler, it works quietly, some functions are missing, it is better to use the old firmware V3.4.104_build190424.
DS-7608-K2 - better NVR with better firmware. I don’t know about the cooler.
DS-7608NI-K2 and DS-7616NI-K2 - price difference $ 14,20 in my...