I upgraded my old Brother MFC-9970CDW to the new MFC-L8900CDW this weekend. It was being shipped FedEx and was scheduled to be delivered on Monday, but I called FedEx and was able to pick it up on Saturday. I spend about an hour configuring all the options, installing additional paper trays (1 250-sheet and 1 500-sheet), and testing the printer. It's a big improvement over the MFC-9970CDW, which was a workhorse in our home office.
The printer is much quieter than my old one and when compared to other brands. There is a quiet setting that makes it even quieter, but this occurs at the sacrifice of some speed. The fax machine is pretty standard for all faxes. I was able to fax without difficulty using the normal compatibility setting via a Cisco adapter that converts analog to IP for RingCentral.
I am very impressed with the L8900CDW's ability to customize scan functions. Perhaps this was present on the 9970CDW and I didn't explore it. I have mine configured with icons to scan to my iMac's desktop, scan to my personal email, scan to my wife's email, or send to a fire department where I'm medical director.
The quiet function is great (definitely can tell a difference), but it is slower (took twice as long to print a test 30-page PDF).
Also, Amazon Dash Replinishment isn't active yet. This printer isn't listed as a supported model. I emailed Brother USA and was advised it's too new and will be available soon.
Overall, this is a great printer. One of the best multi-function machines you could buy. I highly recommend it!