I have a history of A-fib and currently wear a series 3 with LTE and use the KardiaBand ECG sensor band that I purchased for it. I am considering upgrading to the series 4 LTE and just using the built in sensor in the series 4 instead of the KardiaBand sensor. Would anyone who has used both please comment on the reliability and accuracy of the AW4 ECG sensor where this is concerned? I am really looking to be able to have a completely water resistant watch as the KardiaBand is not water resistant. Accuracy and reliability are obviously key for me. Thank you.