From a UI perspective, it is very intuitive to type in a product model number and it appear immediately in the Product search filter. 
However, I argue it is just as intuitive to type in the manufacturer or description and expect that to appear in the search results. It isn't often that everyone remembers very specific model numbers and it is clunky (especially on ultrawide/high res screens) to have to click the drop down and switch manufacturer just to see all their products and sift through their lineup.

Could the search for products not incorporate all fields (Manufacturer, Model Number and Description) in its indexing?