Potentially powerful extension let down too badly by lack of document/support - unusable by newcomers except simplest cases. Rated 1 out of 5 stars
Hopeless, just hopeless.
Tried to set up a script to modify the headers of a page on loading. Tried to select HTML container and got an error that it didn't match the URL. Why not? No idea. Help pages? Can't find them. Guidance on modifying elements that can't be pointed at by the mouse (eg hidden elements, headers, etc) - none.
I haven't tested it further, it doesn't let me edit pages except the parts that can be seen, and the help is non-existent except for the most obvious parts that don't need help anyway.