The OWC ThunderBlade is still v.expensive per TB, especially in the larger sizes a great many are looking for in a single volume RAID drive setup.
But it is QUIET (using passive cooling)! AFAICT no other multi-bay NVMe box exists that is quiet, certainly not their (actively fan cooled) 4M2 one that's for sure, which most reports say sounds like a plane taking off its so badly designed (crap fan+rattling box). Avoid.
I wonder if one could shuck these ThunderBlade's?...
Buy the 1TB ThunderBlade ($700), remove the low capacity NVMe's (4x 256GB), and then replace them with cheaper ones (eg. 4x Corsair 400/600's NVMe 8TB's recently as low as $700: $2.8k) = $3.5k total ($109/TB).
Not cheap, but still not bad at current prices – especially compared to OWC's own $5.5k pricing which is way overpriced right now.