Installing a third-party Google Drive app requires allowing the app to access your account. An "Allow Access" window is presented to you to permit or deny the completion of the app installation process.
Several of the apps I installed and tried have well designed interfaces and are remarkably functional. Gantter, for example, will look and feel comfortable to anyone who has created schedules and Gantt charts using Microsoft Project.
Saving data from a third-party app to Google Drive requires authorization the first time. This is the end of the access-granting process, however.
Like the installation process, permitting initial file saving to Google Drive requires a separate "Allow Access" acknowledgement.
Page 3: Problems with the apps...