I have looked at AOMEI's product, but I do get concerned about Chinese written software. Maybe my tinfoil hat is on too tight, but I always think "TANSAAFL" when I see "free" products.
You are right about differentials versus incrementals. I handle this at home by having two home networks. One for Internet traffic, and another network card and switch for iSCSI. This way, machines can back up to the Windows server, and the server OS can do deduplication in the background so 10 full backups of the same data get replaced by one copy and 9 pointers to the real data. This is definitely not enterprise-grade, but it does work for backups. Since the iSCSI target stores the data in disk images on the server, the underlying filesystem only has a few large files to worry about, as opposed to millions of small files and directories. Every so often, I dismount the iSCSI images so the OS can stitch duplicate data together without worrying about open files.
Since my relative only has one machine, I think I give Acronis a revisit when they get out their latest version (most of the time they just put out a new version so they can get upgrade fees, but maybe what I encountered was an edge/corner case, so it might be fixed.) It is only 30 bones for an upgrade. To be sure, I think I might also have a second drive that has a task that runs weekly to monthly to run wbadmin and do a dump that way. This way, if TrueImage fails, the documents are still protected by Mozy, and there is a fairly recent image of the entire machine, so I can still recover.