Any medium can fail, and if you need something and get it easily any other way you should have backups, not micromanaging which one fails more, CMR or SMR.
HOWEVER, when discussing cost effective and hoarding the best price/TB is by far for larger disks and larger disks aren't SMR, problem solved.
Actually that would be ONE (probably the only) use for the MyCloud things where you can enable ssh, and it comes with a usable ssh with sftp subsystem (can be used as rclone backend) and rsync binary (you can do rsync over ssh). Not that is for the MyCloud without "Home", which are much more "cloudy" things.
Otherwise of course anything else that has USB (and the network you want, wired or wifi) and runs ssh/rsync would do, including Windows if needed but most likely a Raspberry Pi or something.
Not a great plan, and hardly worth the bother for a few disks. For Linux the canonical solution is mergerfs, and for Windows Drivepool (paid). If some redundancy is needed snapraid (runs natively on mostly anything and is absolutely best fit for some collection of media).
Yes.
The answer is ALWAYS 42!
What else should I consider to make an educated decision?
At first what you want to do with them? Do you want blazing fast network access for video editing? Do you want to run a Plex server? Nextcloud? Synology Photos (or anything else Synology offers for sync or something else)? Or photoprism/immich or similar? And so on ...
I wasn't suggesting to run it on the image, just to have the image for reference before doing unpredictable things you can't undo, but if you want you can run it there too for a test (even better have a reflinked copy so you can play as much as you like). It'll just flag/correct if possible whatever inconsistencies you have in the filesystem, with its native tool. What's wrong with that?
NEVER do that
But what, run the mac something?! NOTE: everything I recommended is AFTER YOU MADE AN IMAGE OF THE DISK!
yea, sure, kill it completely
Well, if it's dead already how you can confirm it, at least to take out of circulation?
First of all you don't run things that irreversibly change the disk you're trying to recover data from (I mean before making a complete image of the disk). Second you shouldn't be trying to fix some exFAT file system with a Mac disk utility. Use a Windows machine and chkdsk. For good measure you can do a surface scan too, in case this is where your problems are coming from (HD Tune for example in Windows, badblocks in Linux, I'm sure Mac will have something too).
Anything rclone supported.
Fully recycling my comment about another Synology, here being even worse at 3281 Passmark CPU, probably they don't put in Coke machines CPUs this lame nowadays.
Unless I'm looking at the wrong box it's a Ryzen (so no hardware accelerated transcoding) with a very meager 4584 Passmark? That's really low if you want to actually do anything with it, I mean you wouldn't start building a PC anywhere close to that weak, heck even the ultraportables like Surface Pros are multiple times more powerful than that.
You can shuck it anyway, if you mean if you can access the data in the same way without the enclosure, with large/new drives, yes. There are some (older/much TB-smaller) enclosures which have encryption in the enclosure, and the content of the disk is actually encrypted all the time even you don't set a password (so you can flip the encryption on instantly) but here it isn't the case.