To enable autocomplete in Speedgrader, you need to install the The Marking App extension, found here. Once installed, you can use the extension to quickly insert comments into Speedgrader.
After searching for a comment, you can either click on the comment or
press enter to insert it into the Speedgrader
comment box.
You can press backspace to stop the autocomplete
suggestions from appearing.
To change the page, use the extension's popup menu to select a different page. You can also disable the extension here.
Comment usage will be tracked the same way as in the The Marking App web app, so you can still easily check who's making what mistakes.