To answer the original question, as far as I’m aware it is just a very sensible suggestion.
The drives should work using their provided USB interface without any issue, but it will be far slower than using a USB 3.0 interface.
The hard drive enclosures are effectively just protective boxes with an included USB 2.0 adapter. Removing the drives from the boxes and using a SATA to USB 3.0 adapter will give you better results, particularly if you are going to use this NAS for media streaming, where the transfer rate may actually become an issue.
Hard drives have physical limitations based on their design. Rotation speed, chips used, etc. Using a faster interface may not increase the transfer speed very much. This what I have found with some old drives I tried to resurrect, in the end the transfer rate was too slow for my liking.
Even new rotation drives are no where near what a SSD will do.
Just my 2 cents
Cheers
Jim