Best plank app I have tried

I have downloaded about five-seven plank apps and this is the one I am sticking to.
Main thing - you can choose the exercises and how long you do them.
Four stars instead of five only because of a small bug - when you change the interval between exercises you can not go back to the app, you have to shut it down and load again.
Another desired feature - for the app to be suggesting new lengths of app once I reach a certain level but this can be done manually, so its a minor issue.

kara_sev about Ultimate Plank Workout - Create your own routine or use an existing one, v1.0