If you're looking for fast, dual-drive external storage, the $250 TerraMaster TD2 Thunderbolt 3 RAID enclosure is as good as we've seen. It supports hard drives and SSDs, though there are far smaller and less expensive enclosures for the latter.
The real question concerning the TD2 and other two-drive boxes, is whether Thunderbolt offers enough of a performance gain over USB 3.1 to warrant the price premium. Similar performing USB enclosures, including TerraMaster's own d2-310, are about a hundred bucks cheaper, so it's a valid concern.
