Ive always heard this recommendation. How does this work, exactly? You plug a PCIe that spits a (proprietary?) cord out the back that connects to the shelf that has drive caddies and controllers? or does it work through the LAN cable?
The HBA is just a PCIE card that can talk to multiple drives on one cable that cable connects to another device that can have a lot of drives connecting to it. There is a limitation of bandwith for the card (Pcie speed) and the number of connections it has to the shelf. Only really an issue with SSD shelfs and for home labs its not really an issue.
Here is a talk about building your own. But they make COTS shelfs you can get.