Fail safe works reliably in my experience - but it doesn't save from risky flight in the first place. I think YMMV, but I've yet to have an in-flight failure that resulted in crashing or losing control. That being said I'm overly cautious about inspection and maintenance of the craft I own.

I'm not disillusioned though - it will happen, I'll lose an ESC mid-flight and I'll have to deal with trying to guide an uncontrollable aircraft that I may not have line of sight on. Pretty much next to impossible to guarantee anything in that situation.