I personally use the most recent canary (alpha) versions MOSTLY without issue (just stay away from 2.0.3.6 and 2.0.3.7).
For my clients I use the most recent beta version without issue.
Duplicati 2 has been in beta for a long time (not quite Gmail beta long, but longer than many applications). For something in “beta” it is VERY stable.
While a forum isn’t necessarily the best place to get an impression of software (because most of what you see are users reporting issues) consider this.
Last month (May 2018) there were 124 new topics created on this forum (including How-To guides, Release notifications, etc.) while the following backup counts across all versions of Duplicati (including bleeding edge canary versions) were logged (for installations where usage reporting has NOT been disabled):
- 1,615,430 Windows
- 292,616 Linux
- 71,514 OSX
For me, that low of a reporting rate for that high of a usage implies this is pretty safe software.
That being said, what I’ve noticed is for any particular installation it either seems to work really well (for most users) or terribly (for very few users) - in both cases pretty consistently.
My best suggestion would apply to ANY backup tool (including Duplicati) - just make sure you TEST your backups from time to time. And remember, while a process like How to test / verify your backups is good, NOTHING beats an occasional actual restore and file comparison.
Not only does it give you peace of mind that the backups are doing their job and are viable, but that YOU know how to do a restore if one is needed. When the boss says “I deleted that one file I need for my meeting in 20 minutes” you should feel confident you can get it for them - maybe even with an estimate for how long it will take. 