What does Clustrix offer that MariaDB Cluster within its MariaDB TX offering not?
I believe the main (and only?) purpose of Clustrix is sharding, which MariaDB Cluster doesn't provide - with the provision I suppose that multi-master is strictly -not- the same as sharding.
Not exactly. With Clustrix, your application isn't aware of the data partitioning. Instead, the query compiler creates a multi-stage program that forwards tuples from one partition directly to the next, with only the result set coming back to the node the application is connected to. Applications can connect to any node within the cluster and issue queries (usually this is done through a load balancer).