Good points I had considered but ‘quick and easy’ gets high points in my world. Pros and cons need to be weighed.
Well, an external SSD (or even a USB-C flash drive) as an “available at any time” data drive is quick and easy INITIALLY, but a hassle over time.
I in fact have a Lenovo Thinkpad Netbook for which I use a 256 GB micro-SD card in the (external) micro-SD card slot as the data drive. (Similarly, my old HP laptop’s SD slot got used with a SD card as IT’S data drive.) But of course then that slot is tied up, so if I want to transfer, say, pics off a micro-SD card onto my “data drive”, I have to have a separate USB card reader on hand, with the attendant somewhat slow speeds in play. A few years back I used an external HDD with the employer supplied laptop from a company that employed me as a consultant — I never did forget to take it on a trip to their facility, but... Plus it’s just more to lug around while traveling.
In 2022, a high-reliability micro-size flash drive (maybe Samsung makes one?) permanently left in a USB-C port would make sense, but this laptop has only one USB-C port.
So, what I’m looking at is “quickest and easiest”... as judged over the life of the machine.
Reliability / life of the boot / programs drive is also a consideration: Less use of it, and keeping most of it “empty”, should prolong its life.
Of course if it just can’t be done, requires a different motherboard, etc., then the advantages over time of a 2nd internal data drive are outweighed or just plain sunk. :-(
As it turns out (see my post just above), adding the M.2 SATA drive in the WWAN slot was fairly easy, although I did have to learn how to initialize the new SSD for File Explorer to recognize it (something I’ve not run in to as such when cloning drives in the past - maybe the cloning software just took care of it.) The initialization is easy once you know how to get to it via device Manager.