Actually, SanDisk described the 550 MB/s as the data transfer rate. Internally, a SATA interface was still used, which is how the limit comes about.
+ I don't notice any difference between reading and writing when I use the device. I have not tested this either.
- The SSD gets warm in use (not hot) but is otherwise very pleasant to take with you every day.
+ Has a USB type A to C adapter
See:
https://www.computerbase.de/2020-09...

But there is a new "Pro" version that is even faster thanks to NVME:
old: Sandisk Extreme Portable (2000GB)
new:
Sandisk Extreme Pro Portable (2000GB)