To see the suggestion, you should right-click on the underlined word and the context menu should appear (quickly). In the menu, there should be a list of suggestions and an explanation of the error. Red lines are for misspelled words, and yellow for other mistakes.
An older version was slow, but that should have been fixed in version 0.0.5.
My problem is that the suggestion don't appear on the context menu, but the errors do get marked. However, it works if I install the plugin from the advance settings.
I'm taking holidays in February, so I wouldn't be able to check make new changes until I'm back in March.