Tellico, the soundboard is the curved piece that the reed sits/vibrates against, and is the primary dictator of the call's sound. Much like in the instrument world, they work just the same. I understand the confusion though, it looks like Hut just calls the whole thing a "reed assembly", which should be more correctly called an "insert", with the part you blow into, the "barrel". The sound board is (part of) the reason very expensive calls are often regarded as "better" than many of the less expensive, mass produced calls. Most of the more expensive calls are CNC'd (or hand made sometimes) to a very specific shape, to garner a very specific sound, where most cheaper calls are injection molded (like the Echo and Hut) which are far less expensive to manufacture, but yield far more inconsistent products.
I've not tried the Hut version, but have built quite a few with the Echo insert, and found the primary problem to be inconsistency. I have one or two of the Echo inserts that have a wonderful sound, but I've gotten many inserts that just sound like ****, no matter what I do. Maybe I'll have to try one of the Hut versions.