Natural Cycles App

Hi! I've just come off the pill because it wasn't a great method of contraception for me and had a ton of side effects from it. I like the idea of Natural Cycles because you're not putting any pills or hormones into your body! Has anyone tried it?? I'm weary because occasionally my cycle will mess up (travelling, stress etc.) so not every period is totally regular. If I used the app would it still be effective?