WazzapMigrator converts your old iPhone WhatsApp Archive (Chatstorage.sqlite) into the Android WhatsApp Archive (msgstore.db). Messages are split in chunks of 2500 messages each in order to avoid overloading your phone and convert them a piece at the time. Please note that WhatsApp restores messages on first run only, thus forcing the user to "trick" him by reinstalling or resetting WhatsApp.
If you want, you can also merge pre-existing Android WhatsApp archive (msgstore.db.crypt5 or msgstore.db.crypt). In order to do so you need to decrypt the Android archive, then WazzapMigrator will work its magic to merge the old archive with the new one.