Are you a Mac Mini Dock / 8in1 Dock / SSD Enclosure customer of ours & also an M1 chip computer user?
You might want to take a look at the SSD compatible list attached. Especially if you're looking to purchase an SSD that would be used in a Mac OS environment / with an M1 computer. As there are numerous reports of M1 computers do somehow limit the WRITE speed of an SSD while the READ speed is normal. We strongly believe that the issue would be corrected in the next Mac OS update, hopefully. Do note, even the SSDs listed as "COMPATIBLE" ones, the WRITE Speed might still be limited / degraded if used with M1 computers. We suggest that you have a look at the forum links below before getting your SSD for storage expansion.
Should you decide to try out the "Compatible" ones on the SSD compatible list to see if it works without the WRITE SPEED LIMIT on an M1 chip computer, please do purchase the desired SSD(s) from an SSD seller that allows return if the purchased SSD(s) is somehow under-performing or showing lowered WRITE speed due to M1 chip WRITE speed limitations. We do not accept product return if it's solely for the reason of WRITE Speed Limit on an M1 chip computer. In which it's something that Mac should be rectifying.
So far, we do know that Samsung 970 Pro, Samsung 980 Pro, Corsair MP400 SSDs are working well and not affected by the WRITE speed limitation on M1 computers.