What's the usb port speed and type? Is it usb3.1 with thunderbolt 3? The description says: "two Thunderbolt 3 ports for speeds up to 1556MB/sec" when tech specs: "Max. data transfer rate 5000 Mbit/s"? On the other hand Thunderbolt 3 specs guarantee 40Gbit/s. Info provided in the descr is very confusing.