Here's my experiences......since I've taken all the *weird* options....
My main 486 uses an actual 128GB SSD - full on 2.5" unit - on a SATA to PATA adapter, through a PTI-255W Super I/O Controller (WBIDE is the DOS Driver so IIRC off the top of my head here, a WD chipset). It ROCKS! I use the 128GB for FreeDOS 1.3 (or whatever the latest version of FreeDOS happens to be). That's acutally the drive I use most of the time. Yes, I have full capacity, 32GB each Partition.....so much space (but much needed as I use SHSUCDX to virtualize most of my CD-ROMs/DVDs to save wear and tear on the real ones).
I did get one of those super cheap mSATA adapters for it and had some luck with mSATA but I got read/write errors on the 486, and the original intent was to use them on the NEC Versa and NanTan FMA9200 - problem was, they don't really work with the laptops at all. It was a very cheesy $8 affair though so maybe with a higher quality adapter the mSATA drives would like to play nice. I know when one of my laptops dies I'll have an extra 128GB or 256GB to play with.
I've been toying with getting an m2 reader of better quality and trying it out - I have an, uh, resource of 16GB Optane NVME drives that I Could snag one or two to play with for giggles. Not sure how well those might play ball though given I've heard some, uh, *things* about NVME drives.
The speed is comparable, maybe a hair better, than one of my ATA-100/133 setups on the same system (all of the 486 machines have ATA-100/133 drives in them most of the time save for the desktop that has the SATA SSD). Windows 95 on a SATA SSD is about 34 second boot time on a 486 DX4-100 with 64MB of RAM, roughly a little bit less in FreeDOS. Last night I was running 95 off an ATA 100/133 80GB Drive I have, roughly the same boot time.
For most of these I'm using OnTrack 9 for my DDO, mostly because I can install the O/S by booting off the DVD-RW Drive I put in the 486 (my 486 has a 5.25" Mobile Rack that I use as a literal O/S playground).