Sorry to pour water into the wine as well. But with the latest version of iMazing (like with iXplorer), still 'as of iOS 8.3, only Apps with "File Sharing Enabled" can access the Documents folder'. That's what the error message says here.
Better than nothing, but you still don't have general access to folders and subfolders like you used to have before. Meanwhile I have downloaded a file which would enable downgrade, but looking for a way to get my 8.3 data backed up: 8.3 backups are not downward compatible.I will never again install an Apple update with any bit of trust.
This is the same company which is impertinent enough to upload aupdates into my iOS devices, via my internet connection, without ANY permission from my side, as if my iOS devices were their extended territory. Unbelievable! No other software company I know has such a bizzare, patronizing way of treating users (and developers).