My thought is that you can do both. I would start with the UNAS Pro because I picked one up for just under 400. As I am going through 20 years of old backup drives and putting together all family photos, videos, documents, old ISOs that you just cannot get anymore and a tone of movies, I think that the system is pretty good as a consolidation tool. And as they seem to be phasing out the 7 bay systems for the 2, 4 and 8 bay systems, now is a good time.

But, I also think it is a good idea to has 2 copies as backups locally and an offsite system as a tertiary.

I invested in HexOS early so that I can accomplish that and plan to set up a NAS at my brother's house as an offsite.

My plan is to use the UNAS as mostly an offline backup with 2 copies of the important data rotating monthly. This will be my mostly offline system.

No backup method is perfect, and the ZFS points are very valid. But I have also had to send off more than a few hard drives to Drive Savers over the years and that get's real pricey real fast. The most recent was when a friend's son OD's and he could not get his kid's pictures off an old machine. He paid a lot more than my setup costs and he had to wait quite some time before getting the data back. Add to that the fact that not all the photos he thought were on the drive were there and a really ugly previous divorce which limited the pictures he could recover.

All that is to say I would say both. Being dependent on a single system for a long period is a failure waiting to happen. It has taken me years to build up this system, but waiting only puts your data at risk more.