We've been using it for 1.5 years on our now 2-yr-old, and it has been very helpful at relieving our anxiety and removing any need we might feel to "go check on" our child because we can see in real-time how she's breathing. The best part about it is that we don't need anything in the crib or on the baby to do it, just the camera, which detects the barely visible movements associated with breathing.
The camera itself is so high-res that we can zoom in and see the breathing ourselves, much better than the other monitor we have. Although our child is past the point where we want to monitor her breathing full time, we still activate the monitoring occasionally, and if I forget to turn off the monitoring before getting her up it will alert me, so I know it's working.
Also, even though it's on your phone, you don't need another "always on" monitor because it does that as well, you can even hear the audio with the phone locked. If our child was still within the risk period for SIDS, this would be very helpful.
The company is also very responsive. I've been using it since it was being beta tested, and they remained responsive even after the beta testing period, responding to feature suggestions and bug reports quickly. Their only agenda seems to be making a great device that parents love and that helps kids, and I think they've achieved that.