I have been using the app for more than a week now and Im quite happy. I use a Scosche Rhythm+ heart rate sensor and they work smoothly together. I bought the all inclusive upgrades, but when I tried to run the fitness test, I got a message saying I needed a "compatible Polar heart rate sensor" to perform the test. I called the Polar customer service. They were very kind and helpful, but the truth is that the fitness test only works in combination with a Polar heart rate sensor (not a compatible one).
So, unless you have a Polar heart rate sensor, dont download the fitness test upgrade. Waiting for an upgrade that makes it possible to perform the fitness test with "compatible" Polar heart rate sensors.
Egnatius about Polar Beat: Running & Fitness, v1.5.2