I work with these guys a good bit. Not a marketing driven company. The founders built the KVM hypervisor, so there's lot of low-level OS optimizations going on.
I found this article really useful in understanding how Scylla is different:
https://www.scylladb.com/2021/05/13/an-interview-with-pekka-...
Also, loads of teams use Scylla as a backend for JanusGraph.