I started out with the free version, on ios 5.1 At first I had frequent crashes, my own anlysis was that you must not skip any step in the process. I concluded tha the app crashed when I changed time settings and then returned to the main scren without saving the new time frame. After training to save first I have not crased again. I really like the interface and could not do without the fine tuning into tenths of seconds. Other ringtonemakers did not appeal to me so i bought the pro version for the advanced options, mainly speedcontrol. I give it **** to give the developer room for improvement, coversion is slow ( or am I trying to push things?)