Are these good for 280 mm radiator for watercooling?

They should work fine the key is more air flow the better to remove heat. I hope this helps.

How many fans can hock to Controller???

I am not using the provided controller, I ordered two other 3-1 dongles and am planning on attaching them to one motherboard header each (RGB & Power). The controller appears to accommodate four fans, but have not tried it since my motherboard supports RGB.

Questions & Answers: Cooler Master MasterFan Pro 140 mm Air Pressure RGB Fan, 3 in 1 with RGB LED Controller. MFY-P4DC-153PC-R1.

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