Not Just Analytics uses Instagram Official API. This means that your profile is 100% safe (we will not ask you for your IG usename and password) and that it will not be penalised by Instagram algorithm. As it may happen with those services that use Unofficial API.
The login with Facebook is necessary to guarantee the right functioning of Not Just Analytics. Since it allows us to analyze the data of those Instagram Business profiles connected to Facebook pages you are administrator, accordingly to Instagram rules.