Just a heads up.
4.2 beta may have a bug with Time Machine backups. It may say corrupt backup, delete the old backup and start again. Did it once for me and a few users on the Synology forum.
Try 4.1 first. Synology's pretty fast with updates and I'm sure 4.2 will be out of beta in a month or so.
OP, the local vendor has a DS213+ @ $425 available. Must resist temptation , there's absolutely nothing wrong with my DS212j 🙂