I would add a word of caution to using Screw Extractors, or "Easyouts"
If the reason the bolt is stuck is the head has rounded off or sheared off then, unless you can free the threads, then a screw extractor will probably not remove the screw.
What can happen is the screw extractor can snap off in the hole you just drilled. This then means that you have a hardened steel insert stuck in the middle of the screw which makes it very difficult to drill out.
I do use these, and used one recently to remove a sheared off stud in a k-series engine, but you have to be fairly sure that there is a good chance that the offending bolt/screw can be removed.