Everyone uses this, so success is good. If you screw up you can always restore with no problems, it may take you a coulpe of times. I would first read through all the posts to see what other problems people had and the solutions to them.
Yes there is a high sucess rate, look at how many people thanked that guy for the post. Anybody can screw up if they don't follow directions. You can update to the latest firmware when it comes out unless you have unlocked your phone.