A:AnswerSE is slightly smaller (1mm) in both versions and it does not have the EKG function or O2 (oxygen blood level) apps but still has heart rate. So you can save a lot if those are not important ( I honestly almost never use them on my S7 watch). I guess if you have heart issues or lung issues then they might be more important - but in a healthy person once you know they are normal there is not much reason to check them.
