A really useful addon!
I favour the Chrome functionality also.
If double-clicking is not an easy option, I would favour the 'Highlight word' menu item to have the functionality that shift right-click menu item has now.
So however many highlights I wish, I just choose the same menu item.
If I ever wish to change from just one word to another word, I can 'Remove highlighting' between choices.
This also makes all the major functionality clear. I do not favour any a separate options section to choose, except for quite advanced options, and this may be best accomplished by a separate app.
Conclusion - great now, can be improved.