I’m not going to delve into all of the things you can do with a Synology device, but I would recommend you check out a recent post from Casey Liss. You can also search the archives of MacDrifter for a wealth of knowledge.
TL;DR: they are extremely versatile. My reason for getting one was the ActiveBackup for G-Suite add-on package (free). I manage a 200+ person G-Suite domain at my day job, and I sometimes worry about files getting deleted by accident. I had been using Spanning to backup some people, but it wasn’t cost effective to do everyone.
By using the DS418play and 4 4TB NAS drives, I was able to give myself 10 TB of backup storage (using Synology Hybrid RAID). We have about 6 TB in use, so this gives me room to grow. Setup was a little tricky (it involves Google Console Developer), but I was able to get it going in about a half hour. The overall interface is easy to understand. You can pick users (all or just a selection) and pick the backup time (automatic, nightly, weekly, etc).
Considering there are no recurring fees, this setup is a great idea for heavy G-Suite users. You can pickup a DS418play on Amazon for $429.99. I recommend NAS specific drives (they are meant to run 24/7). Seagate has a 4 TB model for $123.44