Does this app have its own data store that it syncs with iCal or does it just use the built-in calendar data store? I am always much more skeptical of trusting

Does this app have its own data store that it syncs with iCal or does it just use the built-in calendar data store? I am always much more skeptical of trusting yet another app to sync properly (no duplications, lags, etc). These apps tend to make life harder since I have to deal with their issues rather than just being a better interface to the same data. I'd love to know.