Honestly what really matters (imo) is that you do offsite storage. Cloud, a friends house, your parents, your buddy’s NAS, whatever. Just get your data away from your “production/main” site.

For me, I chose cloud for two main reason. First, convenience. I could use a tool to automate the process of moving data offsite in a reliable manner thus keeping my offsite backups almost identical to my main array and easy retrieval should I need it. Second, I don’t really have family or friends nearby and/or with the hardware to support my need for offsite storage.

There are lots of pros and cons of each, let alone add your specific needs and circumstances on top of it.

If you can use the additional drives later on in your main array, some other server or a different purpose then it may be worth while exploring the drives (my concern would be ease of keeping offsite data up to par with main data). If you don’t like it for one reason or the other, you can always repurpose the drives and give cloud storage a try. Again, the important thing is to do it in the first place (and encrypt it client side).