In my mind app support is the main reason to pick Synology. They may not always be as capable as the best self hostable and/or commercial alternatives, but they are easy for people with intermediate skills to set up and maintain. That makes them a good deal for prosumer homes and SMBs without a dedicated IT guy. And with the way the Synology apps are designed you're then somewhat locked in.

You can get basic network storage more or less anywhere, for much cheaper, so in my mind apps and the polished GUI + integration are the only reason you would even consider Synology unless you're already locked in. Maybe technical support contracts at the higher end, but you can get that, done better, from other vendors too.