M2 isn’t much more expensive than HDDs anymore. It used to be five times times the cost. Now maybe 1.5 to 2 times. And they require a lot less space and no dedicated backplane with seperate power.
Also you need redundancy. A 20TB hdd is very expensive and usually very overkill. Rebuilding them takes very long if you ever have corruption issues, along with other problems.
It’s better to have three smaller drives than a single 20TB one.
Unless you’re running an actual datacenter with cooling and big rack space, m.2 is a likely more worth it these days for a small home NAS.
Things inspired by Ford:
Cars
Adolf Hitler