I have only had persona; experience with one automatic knife - and it was not a good one! I received it as a birthday gift and carried it (legally) for a while. One day while waiting to be seated at a restaurant my wife turned to me and asked why I had blood dripping from the top of my leg - I looked down and was shocked. The knife had partially opened and the very sharp pointy tip of the knife had cut through my pocket and stabbed me. Just a small puncture wound but a wound never the less. The safety on the knife had broken allowing it to deploy. I called the company, they apologized and mailed me out a replacement part which I installed.
Fast forward a few months later the safety broke once again and when I reached into my pocket to pull out the knife it cut me again! That was that and I got rid of it! I am sure there are many that are designed and built better than the one I had, but quite honestly I have no issues with opening my Spydeco Delica with my thumb. Maybe not quite as fast - but fast enough for me. Since I look at a pocket knife as a tool and not a weapon, speed is way down on the list of priorities for me. I would not own another one, but will admit the design of some of the better ones intrigues me.