Should I buy a second hand NAS?

Hi everyone, my English isn’t the best, but I’ll do my best. For the past couple of weeks, I’ve been looking to get a NAS, and the Synology ecosystem is the one I’m most interested in. I’d like to set up a Plex server and back up all my photos and videos on it. The problem is the price. To get good performance for Plex, I would need to buy an expensive NAS right from the start. That’s why I looked for a second-hand NAS on Facebook Marketplace. And I found one! A DS920+ for €400. It doesn’t include the storage drives, but that’s not an issue. The seller mentioned it’s 3 years old. I need your honest opinion, guys: How long do Synology NAS devices typically last? Is it worth buying a used one that has been running 24/7 for 3 years, or should I invest in a new one?

Update: Thanks for all the great advice and feedback you’ve all given me! It’s really helpful! I just wanted to mention that the DS920+ I’m looking at has extended RAM. The seller added 16GB to the 4GB that came soldered