I asked one company why a baffle was required around the heat exchanger. I was told it was because the unit couldn't heat the whole tank. Is that standard practice, or are they selling snake oil?

Hey LESKWVO- I appreciate the info so far- but was wondering, what are the exact mechanics involved? What kind of solenoid valves are used? Best heat exchanger for my buck (for 105 gal L-shaped tank)? Filters?? Or is it best to just bite the bullet and get a kit?