A year or so ago, I bought this DiskStation mostly for storing of photos and music. I was using iCloud previously and wanted to avoid the monthly expense, plus I wanted storage access for my Roon server. After a lot of research and talking with friends, the versatility and easy UI made Synology the right choice for me.
I pair the DiskStation with four Western Digital Red Pro 7,200 RPM drives. I don't remember the specific RAID that I chose, however it allows for two drive failures and differences of drive space (thinking of future upgrades). Synology has it's own operating system, included applications, and application market place. It's quite overwhelming the versatility however it doesn't sacrifice the basic functions. You're even able to install virtual machines for nitch purposes though don't expect great performance. I was tempted to use a virtual machine as a Roon server but decided using an old laptop was a better option.
I frequently use the Synology Photos application on my iPhone to automatically upload and view photos. It works well and haven't had any issues with it. I also use the drives as a network drive for my music. I don't have a lot of use cases and if I did have additional needs, I am sure Synology has an application for it.
I looked into upgrading the onboard memory that's used as a cache and found it unreasonably expensive for what appears to be standard memory. Certain third-party memory sticks can work but not officially supported. You'll want to calculate that in the total price if you're wanting to squeeze out a bit more performance out of your drives.
If you're new to SANs and want a device that is widely used, highly support and easy to use, I would recommend a Synology device. You can find lower cost solutions if you're willing to compromise.