Yes I do use them. And I agree the HF ones are really first rate. The quality reminds me of my HF colbolt drill bit set.
When a bolt breaks flush from over tightening, first thing I try is using the bolt head to back the bolt out. (You would be surprised how often this works.) Then I soak it with Kroil and try to work the bolt out with a small center pinch. (This works more often than you would think). If it still won't come out I use a left handed center bit from an old extractor kit that I never use, to get a centered hole started, then I try a left handed drill. If the drill don't catch I step the drill size up until I drill the center of the bolt out to the thread minor diameter and remove the threads. After a little practice and patience this isn't difficult at all, but I sometimes cheat with a small needle file or chainsaw file when getting close to the minor diameter of the bolt. If the threads of the bolt come out in pieces, I'll run a tap down the thread to clean all the **** out.
Never found one that I couldn't get out cleanly, but it does take time. It could take me 20 minutes or more to go through all of my steps above to get a stubborn bolt out. I've had several salt water boats. Getting broken bolts out is almost expected on any project on a salt water boat.
Oh, if the flush broken bolt is a through bolt(like in a car frame) use a regular drill bit, because you want to push the clean threads that are I the hole into the frame instead of trying to pull the rusty threads from the other side of the hole through the hole.
Chris
Here are bolts I removed from the bottom of my wife's car.