it's the official Samsung app from the Samsung app store. 100% legit.
I have 2 of them. one is downloaded from the web. the other is the one I got directly from Samsung.
the difference however is that the most recent version 126.96.36.199 for some reason removed the Blood Pressure function. ECG & Sp02 are still there so the previous version 188.8.131.52 has ECG, BP & Sp02 working.
I have no idea why Samsung's latest version removed the Blood Pressure but I'm sure they will put in back.