That's MOSFET, and yes, it is meant to be bolted to the bottom of the case or heat sink.
In the page itself, there is a reference to a project that this product is based on. If you go there, you can see the whole thing. There are two MOSFET devices that sticks out and are meant to bolt to the chasis. I've seen hundreds of these offers on eBay, including dis-similar designs but all stating it is for the audio low noise applications.
What I got was a PCB and pile of parts. No instruction. The regulator IC was an obvious PULL and recycled parts AND different from the one that's advertised. It was lower rated (current wise) version. It also did not match the PCB. (3 pin device into 5 hole PCB pattern) NO instructions. When I complained, the seller put up a wall but when I pressed on, he quickly refunded the full amount and went away.
I advise caution on these.... or at least expect all kinds of issues.