3 What Differences are There Between the Dedicated Open Drain IO Expanders and This Method?

Other devices with the same device address and the same register set can function the same way if the I2C software were written or setup in the way described in this document. This means hardware dedicated open drain IO expanders and push-pull IO expanders can use the same I2C library if the output register were set to be output lows and then the device were controlled using only the configuration registers.

For dedicated open drain IO expanders, if the code were written to set the device to be an output through the configuration register and then used the output register to toggle between output low and high (can be high impedance) then the push-pull IO expanders can possibly not be able to sit on the same socket and can generate an active high on the output instead.