Portable SSD

Speed is the whole point. An NVMe drive over USB 3.2 or Thunderbolt sustains enough throughput for several streams of 4K, so one small drive holds a project and moves between machines. Cheaper SATA-based enclosures are slower and better suited to archive than to active editing. Sustained write speed matters more than the headline number printed on the box, since many drives slow sharply once their cache fills partway through a long transfer. However reliable it feels, one drive is never a backup. SSDs fail without the warning noises a spinning disk gives you, so keep a second copy somewhere else.