Hello, 
Every QNAP I’ve owned is still in working condition. They’ve all had their RAM upgraded to the maximum allowable, and each one has a QDA-A2AR adapter either for the system or for caching, depending on the model 
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They are all equipped with WD Red Pro drives (SSD/HDD, never disappointed), except for the TS-251, which has a special NAS Seagate ST4000 HDD with ten years ago (which I should probably replace with a WD soon).
Over the years, I’ve increased my backup capacity by upgrading my devices.
My first QNAP was a TS-251, which I now use as a service for my in-laws, who have minimal resource needs, and as a mini-backup for my critical personal data, located 10 km away.
My second was a TS-253A, which now serves as a LAN backup at home every week for some datas (boot sheduled).
I have a TS-653D with a QM2-2S 220A card and a TR-004, which acts as a complete online backup and service redundancy in case of issues, stored at a parent’s house 25 km away. My TS-653D is in constant synchronization, while the TR-004 is powered on via a smart plug manually from time to time to maintain an up-to-date online backup and a reasonably recent offline backup.
Finally, my latest and most complete service unit is a TS-1655, equipped with a QXG-10G1T, QM2-2P-344 card in addition to a GeForce RTX 3050 and a Coral TPU USB. Similarly, this one has a TR-004 connected via a smart plug for a manual monthly backup.
I go a bit beyond the 3-2-1 backup strategy, but at least I can host multiple people in my circle while ensuring reliable backups through direct and scheduled synchronisations. Some family’s photos are from 1960’ / 1970’ and need to be backup efficiently for us.