Yeah, it's a fan, right? It has fins and it spins and stuff, cool, it gets the job done. Well, yes, but be quiet's Silent Wings 2 fans are very unique, and damn are they good. I'll try to cut to the chase without too much extraneous gushing, so forgive me if I get carried away.
Two things probably jump out at you right away. The first is that the frame looks skeletal and not like any other fan out there apart from a couple. The second is probably the grooved blades that give the fan itself a unique overall appearance. The blades are extremely sturdy and relatively thick. The plastic is extremely high quality, and unlike most fans, I'm certain my finger would get the worst of the deal if I poked my finger into the fan while it was running. I've broken a few blades in my day tinkering while my machine is running, but I'd be very surprised if these didn't just slap my finger out of the way like, "get out of here, this space is MINE!" and leaving me with a sore finger and a bruised ego.
The whole chassis is surprisingly weighty for any fan, and both edges of the duct have a thin and almost indistinguishable rubber gasket to damp what little vibration these might produce. Each corner has a snap fitting which allows the usage of a hard plastic mounting bracket for use with standard metal fan screws or a rubber mount to use with the rubber push pins for maximum vibration isolation. You can flip the brackets around so that the edge of the fan duct will sit flush against your case or slightly stood off, up to you. An option no other fan will afford you.
The blades themselves use a tried-and-true tapered design that has, in the past couple years, become the new standard for fan blade designs. be quiet! takes this a little further with their "Silent Wings Technology." The grooves on the fins help keep the air from running out to the tips of the blades which is where most of the noise of a fan is made (swirling air off the ends coupled with the higher speed at the tips). Controlling the airflow means you'll have less noise (which brings up an interesting thought experiment, do you think be quiet! cares about noise any?), and cleaner airflow which helps increase the static pressure as well. It's all good stuff, and it works, as we'll now get into.
The first thing I usually do with a new fan to feel out the bearings is what I call the "free spin test." I give the fan a whirl with my finger and feel any vibration just from the bearings and also see how long it'll spin. These have weighty fins which help give the blades some good inertia, but it feels absolutely buttery smooth and no noticeable vibration thanks to the high-quality Fluid Dynamic Bearing. The only other comparison I can draw is to that of Noctua's high-end fans, and that probably (it won't) be the last time I make that comparison.
Mounting with the rubber push pins is super easy and I like these much, much better than the dangly pull-through rubber mounts. These are also more secure and do a fabulous job of isolating any fan vibrations. Again, I can't feel any with the Silent Wings 2 to begin with.
When the fan fires up it creates a very cool ringed effect due to the fin grooves. I also secretly want be quiet! to break some of the simple understated design language they've employed and please my past 14 year old self with some strategically-placed LEDs that could really create a cool lighted effect on the fan.
In the past, the likes of the Noctua fans were my silent-but-still-moves-air benchmark, as they were about as quiet as I would expect to be possible without being worthless. Well be quiet! has told their Silent Wings 2 to be exactly that, and you'll say to yourself, "Wow. These really are silent. Wait, have I gone deaf? No, I can still hear my GPU whirring. I wonder how I can shut that up too." And then starts the creeping obsession for silent computing, or the satisfaction of being one step closer to achieving it. But seriously, at about 16 dBA, they are about as loud as a house in the woods on a perfectly still night with a pillow over your head.
These really are dead silent unless you put your ear up to them to let them blow air directly onto your eardrum. These, however, probably aren't particularly well-suited as heatsink / radiator fans as they don't push air very hard (not very high static pressure), although they do move a very nice amount of airflow for how silent they are. Noctua's NF-P14 FLX fans spin a bit faster (up to 1200 RPM, 200 RPM higher than the Silent WIngs 2) which makes them about 3dB louder (like comparing how loud the moon is to the sun to you right now) but delivers about 50% higher static pressure, which makes the Noctua fans better-suited for use in their heatsinks.
The Silent Wings 2 would thus be best-suited as case fans, but given how much I like them, I'd like to see them be able to spin a bit faster, which of course adds a splash of extra noise (which still wouldn't be audible in a case), and also makes them a bit more versatile and allow me to replace every fan in a system with these. Basically, I think be quiet! has plenty of room to boost the performance of these while keeping the fan at pin-drop silent acoustics, especially with their fan design and high quality bearing.