I agree with the learning curve (personally I found it worthwhile, but that's subjective).
But how does ZFS limit easy backup options? IMO it only adds options (like zfs send/receive) but any backup solution that works with any other file systems should work just as well with ZFS (potentially better since you can use snapshots to make sure any backup is internally consistent).
Because you can't use typical back product software. If you do it the right way, you're using my ZFS send and receive to another machine running ZFS which significantly adds to cost.
That's an extremely silly reason not to use a specific tool: Tool A provides an alternative way to do X, but I want to do X with some other tool B (that'll also work with tool A), so I won't be using tool A.
Send/receive may or may not be the right answer for backing up even on ZFS, depending on what exactly you want to achieve. It's really nice when it is what you want, but it's no panacea (and certainly no reason to avoid ZFS, since its use it 100% optional).
I really don't get your meaning of my apparent silly reason. You can't use Acronis, Veeam, or other typical backup products with ZFS. My point is this is a barrier to entry. I disagree that it's not silly for a home user to build another expensive NAS just to do ZFS send and receive which would be the proper way.
Eh... TrueNAS UI basically takes care of any zfs learning curve. The main thing I'd note is that RAID 5 & 6 can't currently be expanded incrementally. So you either need to use mirroring, configure the system upfront to be as big as you expect you'll need for years to come, or use smaller RAID 5 sets of disk (e.g. create 2 raid 5 volumes with 3 disks each instead of 1 RAID 5 volume with 6 disks).
Not sure what you're referring to as an easy backup option that zfs excludes, but maybe I'm just ignorant 🙂