Was wondering if anyone with a TS3+ could test something for me and see if they have the same issue.
Basically, I cannot boot from the USB C 10GBPs port on the rear - The drive does not appear when you power on with Alt held down. The port itself I think is OK because I can access drives connected to it if already in MacOS.
Just tested my Samsung T5 bootable backup via the TS3+ and I get the same situation as you - it cannot boot from the TS3+ rear USB-C port when holding Option (Alt) at startup. It does show up fine within my normal instance of MacOS, and even appears as an option for the Startup Disk in System Preferences, but choosing it then restarting doesn't work either. The T5 does boot from other USB ports on the TS3+.
Maybe get in touch with Caldigit, their support team is very prompt at replying and they might be able to shed some light on the issue for you.
One of the USB-A ports on the rear of the TS3+ is actually on the same USB Bus as the 10Gbps USB-C port, here's a diagram on the Caldigit site:
http://www.caldigit.com/KB/index.asp?KBID=220&viewlocale=1
If I can recall correctly, when I did a Blackmagic Speed Test several months ago using a
G-Technology external SSD, I got similar speeds from that "Group 3" USB-A port as from the 10Gbps USB-C port (using the relevant cables included with the SSD, no adaptor). Both "Group 3" ports were faster than the other 5Gbps USB-A ports, but I didn't take any screenshots or record any numbers sorry. Maybe test it out with your particular external SSD.
I just did some quick Blackmagic Disk Speeds tests with the Samsung T5 (250GB) connected using the relevant USB-A or USB-C cable included with the SSD (no adaptors). Here are the read speeds:
T5 connected directly to MBP = 490 MB/s
T5 to TS3+ rear USB-C (Group 3) = 490 MB/s
T5 to TS3+ rear USB-A (Group 3) = 390 MB/s
T5 to TS3+ rear USB-A (Group 2) = 275 MB/s
The write speeds were a bit unstable and fluctuated a bit (both direct & via the TS3+) so I won't put specific numbers to it, but the write speeds followed a similar trend to the read speeds across the various ports.