I'm the author of iGigBook. You're comparing apples to oranges here. iRealPro is a good app for chord charts with backing tracks. You're not going to have access to the melodies of songs using iRealPro and there in lies the difference. I created iGigBook to be a more complete tool for the working musician. When I created iGigBook I had many years prior to the iPhone existing,created a web based chord chart resource with backing tracks, that site was and is called http://www.realbook.us. You can easily verify this by using the internet archive and picking any date prior to the introduction of the iPhone in 2007.
With thousands of users we haven't heard of iGigBook freezing a lot on iPads and to this date there is no app that's going to allow you to instantly search through various real books and fake books to find a particular song and also provide you with access to chord charts that you can transpose, all in one app.