Pros: I bought these looking for something without LEDs that would still allow some light through from the front of my case. As such, these work great as front intake fans. They move a lot of volume without much noise.
Cons: Audible at max speed, but that is to be expected
Summary: The beauty of those fans is in their quiet function, in addition to their constant spinning. Would definitely recommend if you're planning on building a quiet computer. They are also quite adequate on providing internal cooling to your system. Depending on your chassis, you could replace the existing fans on the chassis with those things...if you want a super-quiet computer. And I've read that they have detachable fan blades...which would make maintenance easier.
Summary: My computer was noisy! Last year I put two brand new fans in it and one of them died after a month. So far this thing is awesome! My computer is now so quiet I can sleep without the noise of it bothering me anymore! YES!
Summary: Bought two of these to replace the fans on a Cooler Master Seidon 240M. One of the two fans that came felt like it was catching as I was manually spinning it... Generally a sign of the bearing being bad (at least for me). As soon as I turned it on, sure enough that was the case - you can always tell by how loud it is! RMAed that for a new fan and now both of them are running dead silent in my case.
Summary: I've purchased and used several different brands and models of case fans, and this one ranks in the middle of my experiences. They are very quiet, but with that "silence", comes a significant loss of cfm. It is far quieter than my cooler master fans, but doesn't put out nearly as much air. I purchased 2 of these, and one has been relegated to a gentle bottom of my case intake fan, and the other sits in a box. I'll be sending these back.