yes it is, as well as a piece of dedicated RAM. In both cases it will store some files (like 0.00000001% of all the files) in the cache, but it will not store metadata / file table, so no speedup filewalker that needs to read all millions of files from the HDD itself.
Whereas Storage space does. I tested both on the same hardware, Primo = blazing fast file write, slow random file read (used space filewalker 7 hours). Storagespaces - fast both (used space filewalker 4 minutes).
(bit offtopic here, mayber better to move to Ways of speeding up filewalker on NTFS)