How does anybody know you won't sell this information or "share" it with "partners"?
Will you say "Judicial warrant or GTFO" if Uncle Sam shows up with a subpoena or a national security letter and demands records?
If my wife and I were in our twenties or thirties, we wouldn't want to use something like this to make appointments with her OB/GYN lest the information be used to police her over healthcare in which neither the state or God Himself has any legitimate interest.
I know that sounds paranoid. I'd agree if the US wasn't looking at another Trump administration and at least two years of Republican control of Congress.
This app is inherently untrustworthy given the political climate.