I have not tested (and will not be testing) the grove, gravity, or card-edge slots. I might be able to test the full-size Stemma later, or maybe someone else will verify on a different device.
As to Qwiic / Stemma QT … works great using one (and two) I2C SeeSaw devices connected via a Qwiic / Stemma QT port, using 5V / 100mA (5V / 200mA), following the I2C SeeSaw details post noted earlier.
I’d call this a success for Qwiic / Stemma QT.