Pretty good!
Not as good as an actual stud finder but it works! Here’s something that I hope helps. Take a nail or something metal, and hold it still in one hand. Set your sensitivity to 50%. Slowly move your phone forward towards the nail till it beeps. Take note of how far away it was. Consider also the thickness of the wall the paint, etc as you readjust the sensitivity. Try it again till you get a close-ish approximation of how far you’d be holding your phone from an actual stud in the wall. For me it turned out at 80%. Saw for some it turns out to work at 70-75%. But every phone and every wall is different. Measured several sections of wall and marked each point my phone beeped. Sure enough it formed a pretty even pattern and vertically every stud was around 16 inches apart. Not bad!