Well built. The mounting system works great, even for retrofit. I didn't have to crawl the attic. So quiet I keep thinking I forgot to turn it on.
Some descriptions say it comes with a 4" adapter, it does not. You don't want to do that anyway, 4" would just make it noisy.
It is so quiet that you may forget to turn it off if you set the power switch to Low.
I have to set the power switch to Hi that I can notice the fan is running, otherwise you cannot tell if the fan is on or off and maybe forget to turn it off. It works fantasticly.