Bought this for a customers PC upgrade and he couldn't be happier. He has a small case so I went for a mATX motherboard and the Noctua NH-L9i. This is perfect for small form factor builds as it is very small. Really small.
Small doesn't mean inneffective though as this thing kept his CPU in the low 20's idle, His intention is to use the PC for music production so it was important that the cooler was quiet. This thing isn't just quiet, it is silent.
If you have a larger build you'll probably want a larger cooler, if only for aesthetics. You won't go wrong in choosing Noctua products though. I've built many PC's and they are generally my choice of air cooler.
This is very easy to fit, just pop the backplate on the reverse of your MoBo and screw the cooler into place. Good length on the cable so you can arrange the position to your liking and for cable management.
Overall, a superb air cooler for any build, but small form factor ones in particular.