When you develop your HDR photos with the Exposio mobile app, the mobile data used is about 2.3 MB per photo. So for a property of about 20 photos, it will require 46 MB.
Compared to other mobile apps used on a daily basis, this amount of data is very minimal.
If you do not want to use your mobile data, you can use the Offline Mode in the app settings. This mode disables photo development until you reactivate it. Therefore, you can wait until you have access to a Wi-Fi network at work or at home to finalize the development of your photos.