Synology RAM DDR4-2666 Non-ECC SO-DIMM 4GB (D4NESO-2666-4G)

Four stars because of price, but other than that I have had no issues when using with DS220+. Rock solid

The extra Ram might speed up your NAS for certain tasks, like video recording.

Works flawlessly with the DS 720+. The cost is high for RAM but using another unapproved modul will cause problems. For example; shut downs, data lose, clicking HDDs. Outright system crashes and random freezing.

It works, I now have 4 more GB of RAM in the NAS.

Synology says if you use any memory but theirs your Synology will blow up and no warranty.

And simple to install.

Good, 4 times costlier than Similar product of same quality

This Synology ram has the same specs as the Micron MTA4ATF51264HZ-2G6E1 which you can get on Amazon for $10-$20 but Synology slapped their name on it and their charging $90 for it. If you want to save some money get the Micron MTA4ATF51264HZ-2G6E1 instead. Ive seen Youtubers using the Micron ram on their DS920+ without any issues.

This was a great buy I caught a sale

As stated, nothing more to add.