I've used it a bit on Android. It's important to note that OwnTracks only takes care of publishing your location to an MQTT server (and also subscribing to and displaying other published locations). If you want to save historical location data, and display it on a map, you'll need to hook up some more software, likely this: https://github.com/owntracks/recorder

As far as the Android app goes, I had no complaints. I didn't notice any significant battery drain issues or anything like that.