Question about Ubiquiti UniFi UNAS 2

Hi all, what does AI mean by saying the following: "Using a USB-C drive for primary storage or shared backups is heavily limited by the current software." Is the software any good for using an external SSD without internal disks? Does this work at all? My goal is to have files occasionally on the go as well as the option to share them at home - like I used to with the old router and a stick on it. Later on I will get some internal SSDs of course...