“Roku Ready” actually means that it has a MHL compliant HDMI port that is also rated to deliver the power that the MHL Roku Stick needs: https://www.roku.com/roku-ready
MHL is a 2 way protocol that allows the TV remote to control MHL compliant devices. So one remote for your TV and your Roku in this case and no additional power supply needed.
However, it’s unclear what Roku is doing with the MHL version of the stick. It seems to be unavailable anymore.