Summary: Unlike the DX513 which is based on the DS15XX, this is built on the consumer 2 bay series (DS2XX) thus you don't get commercial build quality. With that said, the unit is silent, fast and integrates perfectly.
Summary: Bought this for back up for my DS214+. It was easy to set up and can be an additional RAID volume or 2 additional single disk volumes. I'm not sure why some are complaining about the plastic housing.
Summary: I have this connected to my 214DSplay, and it works fine. I have 2 4TB WD Red Drives in each unit, and I use the entire 8TB on the main unit, and I back up that data on Volume 2 on this one which is configured in the Synology Hybrid style of things.
Summary: The description says it supports 2.5" drives, but it fails to mention that you need an additional adapter to fit those drives! The adapters are around $10 each which is not an issue, but finding these "type c" adapters in stock somewhere nearly impossible.
Summary: I got this thing set up in about 10 minutes, include hard drive installation and software configuration. For my model Synology, this expansion unit had to add the extra storage as a second volume, so check your model number if that is a concern for you.
Summary: I love all of their products. This allowed me to easily expand a client's DS710+ that had 2x4TB to 4x4TB of storage. Just plugged into the DS710+ with the provided custom eSATA cable and you are good to go. The custom eSATA cable contains thumbscrews that hold the cable SOLIDLY in place.