I was very skeptical of using any extractor after going over multiple reviews for several different types. After going over my options, I decided that an extractor was my best bet of not having to undo hours of work already completed on my car.
I was building a small block Chevy when one of the intake bolts on the Vortec head snapped off well inside of the intake itself. I had received inaccurate information regarding torque specs and the bolt was at approximately 25ftlbs when it snapped.
Before purchasing the extractor set, I had already drilled a hole into the remaining portion of the bolt. Thankfully, I drilled straight and true into it. After using the included reverse bit to obtain the proper size hole, I carefully tapped the extractor into the hole with a standard hammer. Not enough to drive all the way in, just far enough to obtain a good hold in the hole.
Once the xtractor was properly inserted, I used a small (4-6in)Crescent wrench to turn it. I turned approx 1/8 to 1/4 at a time to prevent splintering the extractor and it came out just fine.
The key to using one of these is to get a good, straight hole deep into the broken portion. Don't get in a rush and try to avoide side-pressure - this will break the extractor. Small turns will help avoid improper twisting, etc.
In my case, this tool did exactly as advertised and removed the broken piece.