Conclusion

There is a certain disparity between problems and features here: I personally can do without most of the features but do not like to live with the problems. Additionally, backup is a must have but also not something one gets in touch with often as the processes themselves are automated at least to the point that I as a user only call a script (e.g. connect USB drive, call script, disconnect). From that point of view, most of the tools’ advantages are largely uninteresting such as long as there are no problems!

This is an unfortunate situation with backup tools in general which may be one of the reasons why there are so few good tools to chose from :)

Without further delay, the following table summarizes the findings by recalling the greatest issues observed for the respective tools:

Tool Problems
Borg
– very slow especially for initial backups
   
JMBB
– very slow restore
  – no deduplication
  – no files above 8 GiB
   
Kopia
– no Unix pipes/special files support
  – large caches in Data-Test
  – rather large backup sizes
   
Bupstash
– large file numbers in single directory

My conclusion from this is that Bupstash is a most viable candidate. There are still some rough edges but given that it is the newest among the tools checked that can be expected.