Great if we know the limits

I adore these discs brushed aluminum.
side performance, I did not test the software
disk connected to the USB2 averaged 17 MB / sec write and 25 read
plugged into a usb3 made 25 writing and 36 reading
therefore usb3 improves but in one case as in the other one is very far from the advertised maximum speeds
which were measured I wonder how !!!
That said I have exactly the same results with another 2.5-inch HDD of another brand
So this is not LaCie I questioned, but the performances by all of this product range
when the cable is normally long (the pokey version had a mini USB2 cable) and standard for the usb3