You're usually "just" dislocating the ribs from the sternum (and often tearing the cartilage at that joint). Doesn't feel any less crunchy though...
Exactly! Defibs can't restart a 'stopped' heart. They instead resynchronise the muscle fibres when the heart's internal rhythm has got messed up for whatever reason. They can (try to) fix a heart that is quivering rather than beating cleanly.
But the defibs themselves can sense the difference and won't apply a shock if the rhythm isn't shockable. You should always get one out and let it try to shock if it can.
Coming back to the main point, when I had my first VF episode, CPR kept me alive long enough for the staff at the place where it happened to find their defib. The doctor at the hospital who implanted my ICD told me that surviving an out-of-hospital cardiac arrest was something like a 1 in 5 chance. The surgical team were clearly of the view that I was very lucky to be there. And, yes, I got broken ribs. This was the most painful thing. I had too sleep sitting up because getting up from lying gown was too painful. Sneezing (and laughing) were also fairly painful. But a small price to pay.