You're still bouncing around on what you actually want to do (PM, built-in hardware, number of bays, ...).![]()
It all comes down to what you really need the product to do. If you've a primary storage pool, you may not need to have a redundant backup location (commonly the case; there are instances that backup needs to be redundant, but it's not all that common - think super critical data, or extremely massive capacity where recovery/restoration times are too long to manage without redundancy).
Each of these is a different solution that isn't directly comparable (2 bay unit you linked, 4 bay or other PM based enclosure, or a built-in hardware RAID controller box). BTW, not just this post, but all the posts offered up to you in the thread.
As per Sans Digital's version of the hardware equiped unit, I presume it will work, but I've not had access (tend to need separate cards and enclosures). Areca makes a similar unit (here - in terms of cost too), though you may not like its appearance as much. It will work however, if you need RAID 5 (I stress need, not want, as I have the impression something much simpler will fit your requirements, and save you some funds).
Sorry if I'm bouncing around
EDIT: My thoughts on the two bay unit that I linked (the Sans Digital) is that I could get 2x2TB drives now, and have it in RAID 0 for the capacity I need now, and then pop in 2x4TB when they become available, switching to RAID 1, which would be ideal for my backup strategy.
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