Both have worked well, and supporting software on my IPhone and iMac have been fine. The finger O2 sensor is a small diameter and fits only my small finger with comfort. The ECG AI software is a must for finding errant heart rhythms. If you are monitoring for 24 hrs you will be recording near to 100,000 heart beats; you don’t want to try looking thru all those on a screen for patterns.
ECG, with stick on electrodes, gives good data on a stationary bike, but is erratic when doing weight exercises when in place over chest muscles. Haven’t tried it jogging on treadmill. But tapping it (to make a ‘time point’ in the recording) gives a bunch of noise so I think anything that jars the device will throw off the reading.