Review on GeeekPi 4pcs Raspberry Pi Cooling Fan Set - Quiet, Efficient 40x40x10mm 4010 Fans for Raspberry Pi 4 Model B, 3B+/3B/2B - DC 5V 3.3V Brushless CPU Cooler Radiator (Blue) by Lamar Hopkins

I think it was a great deal! The 2 was $10 at the time of purchase and the 4 was $13, so I figured I'd grab the 4 just in case I get a different Pi later. The 3V fan is virtually silent while the 5V fan is somewhat audible, but even then it's fairly quiet. I keep mine at 5v as my Pi is overclocked and it stays pretty cool. I also love the lights which is one of the main reasons I bought them and they add a nice touch to the Pi, especially if you have a clear case. I would recommend them as 4 packs have the best price.