That means that if a T3 connected SSD works at only half the nominal speed, it's still 50% faster than an internal SSD on a 2013 Pro.Read/Write speed comparison of the internal SSD of
1TB late 2013 Mac Pro: READ ~830 MB/s, WRITE ~830-980 MB/s
2TB 2020 M1 Mac mini: READ ~2900 MB/s, WRITE ~2720-3020 MB/s
as recorded by Blackmagic Disk Speed Test.
Well, quite an improvement and noticeable in daily use! I like it!