This app can be very accurate but most of time time it's not. The problem is mainly the timing. Whatever location it shows, most probably the person was really there... at some point. So the problem is that even if you just spent there 2 minutes it will appear as you were there for 2 hours.It can cause massive arguments.
I would not recommend to use it for couples with trust issues.
Just trust. If someone wants to cheat... he/she will. It's not your problem :)