IIRC, performance was fantastic, but they were never able/willing to match the data density and data cost improvements in stacked-NAND flash, and without forcing themselves into the market at competitive rates, nobody wanted to write applications or design hardware suited to their unique strengths as low-latency caches.
There is still, to this day, a numerical niche for these drives, which is being served imperfectly by either normal TLC drives of very large size, SLC cache drives, or DRAM expansion cards connecting to the CPU through a PCIE bus. Just not at the prices they wanted to charge.
But wasn't the potentially transformative market intended to be "persistent DRAM" for instant-on devices removing the distinction between memory and storage, requiring DRAM-like speed rather than NAND-like speed ?
I recall their early R/W speed performance projections being far faster than what they ever achieved with Optane drives.
The products that used a PCIe X4 interface with a block storage protocol layered on top were never intended to deliver the best performance the memory was capable of.
Interesting - I wasn't aware, but even avoiding the PCI bus the performance must have been lacking as that link talks of "memory tiering". I guess this was "mid tier" somewhere between SSD and DRAM, which is a bit of a no-mans land especially in terms of conventional systems architecture ... really just a fast type of storage, or storage cache (a bit like a hybrid SSD-HDD drive).
There is still, to this day, a numerical niche for these drives, which is being served imperfectly by either normal TLC drives of very large size, SLC cache drives, or DRAM expansion cards connecting to the CPU through a PCIE bus. Just not at the prices they wanted to charge.