I have found the same thing to be true. There appears to be no incremental backup for the local IDrive One device. It took many hours for the full backup (even with a wired ethernet connection). I wish to use this for about 100 GB of important files on my desktop PC.
Incremental backup is not an enhancement request . . . it is a necessity. The lack of incremental backup on a unit like this is a serious flaw. The Idrive One becomes quite useless for my needs without incremental backup. Check your FAQ's. They clearly state that after the initial full backup, future backups are incremental and are a default feature (https://www.idrive.com/online-backup-classic-faq#b115).
I would not have purchased the Idrive One if I had known at the time of purchase that the IDrive One would not do incremental backup.