I have one because a hundful of devices in my rack (switches, AP, Mini PC) are single power supply while the servers are all dual.
Makes it easy to have everything connected to both UPS separately. It came in handy a few times when I had one of the UPS freak out (or when someone decides to flip the light switch that is connected to that outlet, lol). Also was helpful for keeping things only while reorganizing/moving stuff around.
Nowadays I moved everything running in the rack to a mini PC to cut down on power so its not really in use anymore.
Why don’t you connect the ups after the ats? Works great for me (offgrid solar x grid power)
The point seems to be able to handle a UPS failure
I have one, and I love it. It bridges my large UPS and the mains power, so that if either one of those fail, then things keep running. I have it on mains in case something kicks up too high and overloads the UPS.