Although lately something is happening with the supported drives and the list is constantly shrinking, I love Synology. Maybe it's because some (I'm looking at you WD with the RED SMR) have released NAS drives with shingled magnetic recording, which are not suitable for RAID.

I have recommended several Synology devices, I currently manage about 10. Personally, I have the 920+. I haven't encountered any problems for years, I manage everything remotely almost exclusively.

I upgraded my own 920+ with a so-dimm that I had in the drawer. It does display a message that it's not a Synology product during each boot, but it has passed all the tests.

The biggest advantages are ease of use and reliability. It does everything without needing a doctorate. Intuitive interface, instructions, and guides can be found everywhere. This particular model supports BTRFS (in Synology's implementation, which is widely accepted as rock solid), which means snapshots and replication. Automatic snapshots mean that you can restore your files in 2 minutes from anything, even ransomware. You install Snapshot Replication, choose how often and how many you want to keep (e.g. 3 every day, 2 every week, 1 per month, and one per year), and you're ready. SHR, Synology's hybrid RAID, simplifies the process of expanding the RAID and changing disks.

QuickConnect is also a big advantage. You just give quickconnect.to/nasname (nasname = the name you have given to your NAS) and you can connect from any browser.

Active Backup for Business is also a very good and easy-to-use tool for automatic backup on all PCs in your network.

It runs VMs with its own management tool, with shareable links and all the goodies, it runs Docker containers, it's just incredible. Not only because it can do all these things, but because with its tools, all these things run easily and reliably.

A tool for every modern home or office. I highly recommend it.

update 8/2/21
Upgraded with +8GB RAM from Kingston, I don't remember the exact model, but even though I bought one that was said to be compatible and doesn't display any message from Synology, it eventually does display it, but it doesn't affect the functioning of the NAS.
The official 4GB from Synology costs 100 euros, so for the 30 euros that I paid for the 8GB, it's a good value for money, no matter what message it displays!
I have installed 2 cameras in the surveillance station that record 24/7 on the NAS.
The photo I have included is playing with Plex + transcoding in 720 from 4K video.
I have also installed a 250GB SSD for read-only, it helps with the menu in Plex from what I have seen.

15/1/21
It is expensive for a slightly more pro home user! The upgrade from a DS215j was like day and night. Very fast menu, more Plex capabilities, etc.
I was torn between the 720+ and the 920+. If you are thinking of upgrading from another NAS that you have, the 920+ will be more cost-effective than the 720+, because with the 4 bays it has, you don't need to buy 2 new disks to increase your capacity. For example, I had 2x3TB in SHR, so 3TB available. If I bought the 720+ and wanted to go to 8TB, meaning 2x8TB in SHR, I would need 420 euros for the disks + 500 euros for the 720+ = 920 euros, while now I can go to 6TB available with just one extra 3TB disk, costing 90 euros for the disk + 600 euros for the 920+ = 690 euros, and I also have another free bay for future upgrades. Additionally, the 920 has 4GB RAM while the 720 has 2GB.

2nd update Oct. 2021
As promised, I am returning to discuss the
Reliability and functionality of the machine
After almost a year of continuous operation, I can conclude the following:
1. It did not experience any damage or connectivity issues to the network, despite power outages and internet drops, etc.
2. The only maintenance I performed was disconnecting and cleaning it from the dust that accumulates due to continuous operation (trust me, it collects a lot of dust).
3. It notifies you of all the necessary updates, which are easily and quickly done (unlike Windows updates, it's the opposite!).
4. With the new DSM 7 operating system, Synology has become even more functional with amazing security measures, such as two-factor authentication for login, etc.
Additionally, the new applications, such as the Photo app, are very good and make it very easy to organize thousands of photos and tag them. I also use the music app a lot on my mobile, so I have access to thousands of music tracks without burdening my phone.
5. I have installed 4 WD Red 3TB drives, two of which are older (2014) and the system recognizes them as more compatible compared to the two newer ones (2020), which cannot pass the extender test. However, all the drives work fine with monthly healthy reports. The advice, though, is perhaps to use Seagate IronWolf drives, which are more compatible with Synology. I do not know their reliability, but I can assure you that the WD Red drives have been working perfectly for over 5 years in 24/7 operation.
6. The DS File and Synology Drive have become part of my daily life. I can connect from anywhere without any issues. I have almost eliminated the use of Google Drive.
I believe it is worth buying such a server as it makes managing the countless files we accumulate a breeze.

Update Feb. 2021

I am returning after 3 months of continuous and exhaustive testing of the Synology DS920+.
1. It is extremely stable and always there when you need it.
2. You can easily create cloud drives with as much storage as the capacity of the disks you have installed. The Synology Cloud Drive synchronizes instantly wherever you are, as long as there is internet. It's like Google Drive.
3. You can connect to the server and access your files within or outside your network without any obstacles. You just need to create an account with Synology.
4. It can send you emails about its status and operations.
5. The user interface is very easy to use, allowing you to make any desired settings without fearing any problems.
I tested the DS920+ as a media server while also downloading (Torrent) with 2 other connected users (file sharing). In these conditions, the processor never exceeded 60-70% of its capabilities. Although I increased the RAM from 4GB to 8GB, I don't think it is necessary since it operates at 10-20% utilization in normal use. For those interested, the memory I installed is Crucial 4GB CT4G4S8266 DDR4-2666, and it is fully compatible. The system recognized it immediately without any issues.
Finally, I have connected it to a UPS for two reasons: a) to have the server's functions during power outages, and b) to protect the disks and power supply, as I couldn't find power supplies specifically for this model no matter how much I searched.

First approach
The Synology, as hardware, is not the top NAS, but its value lies in its software, which is incredibly easy and includes ALL the functions of an advanced server. It reminds me of the functionality of Apple's Mac OS. You can do everything quickly and easily with minimal knowledge about servers. It is also completely silent.
As for the longevity of the hardware, I will come back to that.