I'm not intimately familiar with the Pi Zero W features but have read that you have to disable Bluetooth in order to use the native UART. So, it would seem the advantage of the hubserialixed is that you can add USB ports and a serial port without losing Bluetooth. It would seem ideal for integrating the various HA technologies as well as peripherals like a keyboard and mouse.
Today's mail brought two packages from referencedesigner.com - one had the HubSerialixed but the other had two boards, each of which have only 3 USB ports. There was no explanation and no documentation. Upon closer inspection I found a
HUBPIWI BLUE label and an RTL8723 chip which does WiFi and BT.
A web search using 'HUBPIWI BLUE' brought me to...
http://referencedesigner.com/blog/get-hubpiwi-blue/6506/which has lessened my confusion.
It appears that you can now use the HUBPIWI BLUE to add 3 USB ports plus WiFi & BT to a standard Pi Zero for $5. While it won't be as fast as the Rpi3B+, it will cost less - especially if you already have a Pi Zero.
I won't have time to play with these for awhile but they sure look interesting.
A bit more web sleuthing turned up the secret sauce used in both the Hubpixed and HUBPIWI BLUE...
http://terminus-usa.com/product/fe1-1s-usb-2-0-high-speed-4-port-hub-controller/PS: I suspect (but don't know for certain) that the BT vs UART conflict is solved with the HUBPIWI BLUE.