aCalendar works both, with cloud and local calendar.

You can create new local calendars in the calendar list.

All calendar data is always stored in the Android calendar storage, aCalendar has no own data. 

When using local data (no matter if it is contacts, photos, calendars, etc) without backup you always risk complete data loss when the device breaks or gets lost. Using local data should always mean to have a proper sync/backup solution working!

You can backup local calendar data in Android by:

In particular, when using multiple devices, we recommend the use of cloud calendars, so you have easy access to your data from all devices and the web browser.