I've bought a few mSATA SSDs on ebay over the last few weeks - 250/256GB for my Linux laptop system disks. All were main brand, a couple of Samsungs and a Kingston (main'ish I suppose). All were relatively low hours and cycle count with nothing to be suspicious of in the SMART data and believable benchmark results. I'd rather buy those than new no-name (to me) Chinese brands - there have been a couple of reports of dead year old Phison ones on the forum recently. I got my used ones for around 10-20% of the price of new no-name ones anyway.
I picked a few 500G 2.5" WD black drives a couple of years ago that had single digit hours on them that were pulls by companies swapping them for SSDs I guess those will have dried up as the laptops will now be supplied with SSDs in the first place. All are still going strong. Oh I picked up a pair of decent Samsung 8GB SODIMMs for one of my Thinkpads recently too, for little money too.
For me, it's a viable route to upgrading as my needs are modest - I'm behind the curve in terms of maximum demand. mSATA isn't being used in new laptops now, they're all going M2 single drive SSD. My clunky old Thinkpads can accommodate 2 x 2.5" and an mSATA so I'm not pushed for drive capacity and have redundancy.
Short answer, it works very economically for me, your needs may well be different.
Edit: I should probably add that the cheaply ebay purchased smaller capacity 128GB Sandisk mSATA SSDs, that were the predecessors of the newly acquired ones, have lived for 3+ years, trouble free and still showing minimal wear.