I ordered the device from Adafruit. The main reason was to check out getting a second I2C device to work. Here's how I wired it from the Pi:
I found soldering the 24 tiny pins to connect the display to the "backpack" a trial, but surprise, surprise -- it worked with their example 24-hour clock program first try. I had previously downloaded --
Most importantly, both of my I2C-connected devices still work. And I can add more. From two GPIO pins (3=SLA, 5=SCL), many devices!