My concern is the 4pin connectors that the CM 212 plus and most stock GPU fans use. The fan controller I'm looking at is affordable and can turn off the fans completely (specifications on newegg incorrect) but it only has 3pin connections. Would it be possible to just plug in the 4-pin connectors into the 3-pins, leaving one pin hanging, would I still be able to control the fan speed as normal?
One of the four pins is just used for polling.
It sends information to the motherboard of what speed, the fan or fans are spinning at in rpm.
You may find you might have to chop off the guides on the connector to alow you to fit it to the three pin connector of the Rheobus though.