As far as I know, atrial fibrillation can only be detected by a doctor with a 12 channel ECG, not with an optical sensor like the GT2. If you need an exact recording of the pulse, I would buy a watch with electrons (pulse belt).
I personally find the loudspeaker very useful when training, you get a warning when the maximum plus is reached.

Hello Christian
I have not used the training myself yet. Basically, however, I would say that you can use the programme "Rowing ergometer" for rowing on the lake and "Free training" for badminton. The heart activity is displayed directly in the training mode. However, as far as I know, there is no ECG measurement yet, only pulse and stress. However, I can highly recommend the watch with regard to pulse. Many greetings and happy new year