At first I tried while it was mains powered (dangerous) but it didn't work, so I used my USB-TTL adapter at 3.3V. My poorly-soldered GND, 3.3V, and TXD, and RXD points were enough to get flashing working.
Those numbers assume left to right if you are looking at the front of the device.
I haven't yet been able to figure out how to get the button to work, but that was less important to me than using a 3rd party, open-source firmware. Hope this helps someone, and any ideas on the button would be appreciated.
Thanks for the teardown, we will add it to templates database.
Regarding button, I can write a script for you later, but if you want just a simple behaviour "toggle All" then you could use Btn_Tgl_All:
Btw, for the sake of preserving information (you never know when Amazon deletes an auction info), I will repost here screenshots of the device from the outside (we have our own reliable hosting on Elektroda, so images here are safe):