Somewhat old, but you can see comparisons on the Duplicati forum (then Duplicacy forum pointing back):
Duplicati 2 vs. Duplicacy 2 (Duplicati comments)
Duplicacy vs Duplicati (Duplicacy comments)
The opening paragraph of the latter points out the risks of storage issues, and what level of checking to do.
Block-based storage engine and Fact Sheet give additional insight into why Duplicati 2 went to a database.
Hanging around the two forums for awhile will show what sort of issues and missing features are reported.