I suspect there's an element of you get it of it what you put in. By that I mean most users only half heartedly use the full range of functions of these apps. If you don't record all your meals accurately in a calorie counter part of a fitness app what use is yay function? If you don't wear your fitness tracker on all periods of physical activity and it doesn't have a hrm function then what point is it?Then there's the question whether these apps really offer anything over a simple notebook and paper or an excel spreadsheet? Some offer some form of coaching and tailored fitness plan. For example fitbit own fitstar iirc which offers such fitness plans.
There's so many tracker apps out there which one is right for you? I'm on strava, Garmin and iirc noom a calorie counter app. I've looked at others too but it comes down to using fitbit with my fitbit Surge but my cycling goes on strava. I don't really look at fitbit app much.My use of apps are to record my cycling. For fitness I monitor myself. I eat what I need to eat and do at least the minimum exercise for maintaining fitness. With this I've started from a good level of health and fitness and it's easy to maintain.