Useless!

First let me say I seldom rate apps - unless they are very good or very, very bad. This app is the latter! I downloaded this app for interval training in preparation for an upcoming marathon. At first, the app worked fine on my iPhone 6s Plus running iOS 10. Unfortunately, I discovered in the middle of a half marathon the minute marker tones were cutting out! In the middle of the run, restarting the app or phone made no difference. From that point on, it was increasingly buggy. Needless to say, dont make the mistake of relying this app for any run you really care about! As for me, I think this has taught me I need to forget about using my iPhone for training and break in and buy an Apple Watch. Save yourself the trouble and do the same!

Mark Winward about Simple Interval Timer, v1.4