Kaleidescape doesn't specify what kind of hardware they use, and there are no teardowns that I can find. But it seems significant that they use the phrase "enterprise-class" to describe the storage in their Terra drives, but not to describe the drives in their players (which would not, after all, have the usage patterns that server hardware is designed for).
Partial correction here! The Strato K doesn't say "enterprise" about its storage, but the Strato E product image does. It also shows a B+M keyed SSD, which would imply a SATA drive. ChatGPT notes that there is a 480/960GB SATA SSD product line that matches the illustration they use, which is an Intel/Solidigm thing. It's since been discontinued, but you can pick up a refurb for $150. I suspect they did in fact use that at some point in the past, but probably they use normal, faster NVMe SSDs now.