The App tries to do more than the iPad is capable of doing. It often freezes and is almost unusable. It needs to do less better. The frequent indexing means that the app is almost never ready when you are.
Logos is a poor book reader app, and there is no reason that it should not be as dependable and usable as Kindle or Nook. Logos can do better. Make it a good ereader first, and then add anything that does not take away from that.
I have a 4th generation iPad, with plenty of room.