I favor Stop ICE which is a website, not an app. They specifically address why:
The Stop ICE Alerts Network is designed to work with technology already built into your smart phone, mobile device, tablet or computer.
Apps on your smartphone can be used by service providers and 3rd parties to access details related to your phone's activity across multiple datapoints. This can potentially open up unwanted vectors for user tracking compromising your privacy while also sharing that information without your knowledge.