Heart rate doesn’t sync. Steps not accurate
Heart rate data is completely inaccurate because instead of using specific data points, the app using your daily average as the input value into Apple health. Resting Heart Rate values are ignored by this app.
Additionally, the step counts from your fibit are ADDED to the step counts that are automatically tallied by your phone, thus the value you see in the Health app will never be accurate. There is no way to select which data source to use for steps, so you just have to tolerate having incorrect numbers.
While is don’t entirely fault the app for some of the issues, it still doesn’t take away the fact this it is entirely worthless as a mechanism of moving your Fitbit data into the health app.