I’ve been using the predecessor to this model for about 3 years now. The DS411 I have has been rock solid and reliable and is highly recommended if you’re looking for a NAS. If I had any problem with that model I’d happily upgrade to the DS412+ for the extra speed and dual ethernet.
These boxes are a good deal for reliable network backup and data redundancy and make a great replacement for an aging WHS system if you’re still using one of those.
The DS operating system has gotten better and better over the years and the current 5.0 edition is pretty great overall with a good balance between simplicity and power.
You can use these boxes for all sorts of things beyond data storage, but at least with the DS411 the speed bogs down with apps like plex, etc. So mainly I use the NAS for data storage, backups and as a music server.
You can also install crashplan on the synology with a bit of a work around and use it as a back up destination as well as backing up your server to crashplan online for extra redundancy!