I'm not that familiar with Synology yet. I know they also have their own DS video
Roku channel, but I don't believe the built-in Video Station on the NAS supports remote player streaming from the Internet, out of the box (without a work-around such as VPN)?
Incidentally I'm also eyeing to get Synology's new DS214play
NAS for family members.
Uses the new Intel "Berryville" CE5335 which is a low-cost SOC based on the Evansport platform -- not as fast as an Intel Atom D2700 for general purpose tasks, but on the flip side has hardware transcoding acceleration (and HDMI support, although the latter isn't implemented in the DS214play unlike in the Asustor AS-302T).
All in all relatively cheap ~$350, although you're not gonna get the peak throughput of NASes with higher-end Intel proc, 3+ drive bays (RAID 5), and link aggregation via multiple gigabit Ethernet ports.
Another drawback is that it will supposedly take some time for Plex/FFmpeg to support
the Intel CE5300-series hardware transcoding capability (in the meantime, Plex would continue to use the general CPU cores to do the job, which would make the SOC slower than standard Atom).
P.S. There's also the general caveat
about runnning Plex Media Server on Linux (NAS):"Many Plex Channels are unavailable when running PMS on any type of Linux host. This is due to Linux not having support for formats like Flash, Silverlight or Webkit video which many companies have chosen to use to stream their content."