Its a good one since, it saves space on your bar. By using it, you can increase address bar, which is convenient, for viewing web addresses.
But, this addon changes the default search engine behavior. My default was 'Google ! Felling lucky ', but now, I can't use it. Every time, I search, it searches from, the installed search engines.
This behavior is changed, if I uncheck 'Enable search without keyword or operator', but then, it does not use any search engine at all.