I'm not familiar with the SimpleTech NAS, and I run 15-25 year old hardware at work so old doesn't bother me, BUT:

1) How many drives does it have? (needs to be more than 1, otherwise it's just an external drive)
2) Can you get the SMART (drive health) status from the NAS? If so, can it e-mail you upon failure of one or more drives? Without this information, you're flying blind.
3) Do you have spare parts (controller/mainboard/power supply)? If any one of those parts goes, you might be locked out of your data.
4) Do you have any other backups of the data? You should, and they should be off-site!

Depending on how you answered the above, I'd suggest going to something newer, at the very least something you can get parts for.

I'm a fan of old enterprise gear. Enterprise customers rotate through equipment quickly, so on the used market it's pennies on the dollar and the equipment is built to be serviceable and reliable. Parts are very easy to get ahold of, even 20 years after they were made. Enterprise servers often have hot-swappable power supplies, fans, drives, even RAM can be changed out without shutting down the machine. Enterprise HDDs are dirt cheap. $20 or so for 3TB HGST(Hitatchi) SAS drives.

If you want to do it on the cheap, get a Raspberry Pi 4 computer and attach a couple of USB drives to it. The Pi4 2GB RAM models are now $35. Low power and quiet. Have a backup of the SD card and if it ever dies just grab another Pi, drop the card in, and you're running. Plenty of information on the 'net and YouTube about turning a Pi into a NAS.