More of an annoyance
So we probably don't really care who's getting the money for the click through but these things are annoying. Recently had the misfortune of using a friends machine which had exactly one of these extensions. Type your search in google and the list pops up as expected and then just as you're about to click on the link the whole page scrolls down while a new list of mostly the same links is shoved in at the top.
Would be interesting to see what happened with 3 or 4 of these installed - browser injector wars! Only the strongest will survive!!