Not as quiet as it claims, but is pretty slim after all.
Using it to cool an AMD Ryzen 5 3600 (the NH-L9i and NHL9a both require a kit to work with AM4 sockets, the AM4 model wasn't available when I bought this). Easy to fit with the kit and fits well. Note that it needs a back plate fitted, so if your case doesn't have a slot cut out you'll need access to the rear of the mainboard to fit it.
Despite its quiet claims and rating being good enough for the chip, it is almost constantly audible. I work from home a lot and need a quiet PC for work. Even just with little more than the browser open I can constantly hear the fan running, and spinning up and down every couple of minutes. Before setting the profile to quiet in the BIOS it was even worse.
It does a decent job of keeping the CPU cool-ish though, so if you have a slim case and don't need it completely silent then this cooler is OK. But, if you need silence and you have the space in your case, get something bigger and quieter for the same price.