I have to admit, I do love the ability to just upgrade the drives and mix/match in my Synology. Recently gone from 4x3TB drives to 3x6TB and 1 3TB drives. Got another 6TB arriving today and the upgrade process has literally been plug and play except pressing the 'repair' button within DSM.
You can do this with QNAP too- Live RAID Migration, i.e. upgrade disks one by one to expand an existing array.
I'm about to buy this too. I take it that it streams everything you throw at it (including 4k MKV rips) to the TV without breaking a sweat?
Sorry, never answered this- currently not using HDMI (the NAS is hidden upstairs to prevent the missus constantly unplugging it). Having said that am considering an HDMI to UTP adaptor as it's right above the TV.