The calendar that comes with iPhones basically ignores most Jewish holidays and all of the other days so important to us - religious Jews, I mean. My husband has a good Jewish calendar app on his phone so when I searched HebrewCalendar Store I discovered this one.
Not only can I use it to find out when, for example, all of Pesach is, this calendar also includes anything I enter into the one that came with my iPhone. This makes things very convenient.
I still use the one from Apple to schedule appointments, etc., because it’s convenient and Im familiar with the many ways to enter events, etc. But if I want to look something up, or need to know what day, month or parsha it is, I’ll come to HebrewCalendar. I think I use it maybe 2-4 times a week. But this is only about a month since I downloaded it.
I won’t be that surprised if, a year or so, I’m using this one regularly and the Apple one only now and then.