Pros: Price to performance ratio is excellent. Flows much more air at low rpms than the Silent Wings 3 High Speed. Beats the tar out of Noctua's redux line for low rpm air flow and silence. This one fan I ordered as an experiment, replace both a NF-P12 1700 and a Silent Wings 3 High speed at the back of my case and still dropped my GPU temps by another 3 degrees and it's loafing along at 50% speed, while doing it. Comes with a nice long cable. Be Quiet has hugely improved the release mechanism for the mounts on the corners.

Cons: Only one snag here. The Silent Wings 4 have the intake side of the fan blades, really close to the fan's frame, so in a pull configuration a person will most likely get turbulence noise from the fans in a draw through setup. Simple fix is some rubber spacer washers. (in a standard blow through setup, this is a non issue) I'd like to see Be Quiet! address this with some included spacers or something for a pull through setup.

Overall Review: Despite the one minor snag, I'd recommend these fans in a heartbeat. They are in the same performance category has Noctua's NF-A12x25 fans but far cheaper and look better than the brown and cream, and come with a nice long cable unlike the Noctua Cromax Black series. I love these. Good airflow at low rpms and quiet both. Much higher static pressure than most fans fans on radiators if you have liquid cooling.