In case OP or any visitors don’t know:
Recertified ≠ Refurbished/used/preowned.
Manufacturer recertified means the drive you get is one that passes OEM/factory testing. There’s a certain QA standard that manufacturer recert drives need to meet.
Refurb etc means you get a gamble drive that probably has SMART data reset so you have no idea what you’re getting. Could be a good deal or a waste of money, very little predictability.
Personally I’d never buy a refurb—I’d only buy recert or something that a trusted friend has used.
The big one is no new feature updates. That includes adding support to new changes in filesystem handling that we don’t know about yet.
Example: sure, NTFS has been on v3.1 for over 20 years, but it’s still being updated in other ways. For example, the journaling LogFile format changed from Windows 7 to Windows 8 and it’s a breaking change—7 and below are incompatible with the new format.
Staying on one version of MR means you’re stuck with that one version even as technology changes. That means you’re probably safe in the short term but aren’t guaranteed things working as intended as you work with newer systems or volumes formatted to work on newer systems.
Even if you pick up MR I highly recommend you look into another actively-developed backup solution if/when your needs evolve.