Per the anandtech article that @AM27 cites: "The technology is...

Per the anandtech article that @AM27 cites:

"The technology is meant to fit somewhere between 3D NAND and DRAM, similar to Intel's Optane storage and Samsung's Z-NAND. Similar to those technologies, according to Western Digital, its LLF memory will feature access time “in the microsecond range”

4DS is claiming speeds comparable to DRAM. DRAM has access times in the nanoseconds (i.e. 1,000 times faster)

4DS openly states that speed is its number one priority. That's why its 21st patent (announced on 22 July 2019) is probably its most valuable one.