The article looked promising but ... I ordered a first that was not working. I returned it immediately (very fast Amazon for a refund, thank you). I ordered a second because opinions were positive and I told myself that I had not had any luck. Unfortunately, the second timer will work properly once in two. I am forced to listen every time if I hear the sound of the mechanism, and if I have to shake it to start. Really inconvenient!
Otherwise, the magnet is powerful and the device fits comfortably on the table. My students have become accustomed to refer and evaluate better the time they have left.