The duplicati plugin isn't reall beta. It is too simple. duplicati itself kind of is.
I haven't used Duplicati since its early 1.0 days. I knew that 2.0 was released but I have never tried it. I ended up switching to GoodSync because I kept having issues with my Duplicati backups failing. Unfortunately though, GoodSync is not free and on top of that, it is out of the question for the OP because it does not support incremental backups.
If I ever have the time and patience to learn, I would like to make an OMV plugin for GoodSync server. I just don't have the time or the patience right now to learn about how to write a plugin for OMV.