I give the replication feature a 10 out of 10. The GUI for snapshot replication gives you a lot of flexibility to schedule asynchronous replication, bandwidth control, and disk-rebuild resource allotment.
High Availability is a 10 out of 10, too, for having redundant RAID controllers per tray and the ability to build an HA Multi-Site.
I also like the easy setup of these units. We get project bids with zero lead time and when you have to build out a facility and you have a deficit of time to do so, it helps to have a quick and easy install and intuitive GUI. Running updates on these systems is nice and easy. The support staff are also very good.