I say "mostly" happy because I almost returned it. The USB connection between mini PC and Terramaster would be fine for a few days and then during intense operations like parity checks would disconnect and look like parity error/disk failure, except the disks were fine. Eventually realised the DAS uses power from the USB port as well as the adapter plug and the mini PC wasn't supplying enough power. Since attaching a powered USB hub it's been perfect.
Explanation of symptoms and solution, in case anyone is considering one or has the same problem: https://forum.terra-master.com/en/viewtopic.php?t=5830