Product review (4 stars): Attractive Hood, Superior Suction, Fair price
The installation instructions are irrelevant for "Under Cabinet" installation, as are the included installation parts, which may become useful for other unrelated projects.
To install under the cabinet, you must remove the filters and bottom cover, which is held by two standard screws at the front underside corners, and one thumb screw at the front center. This will allow access to the key hole slots that can be seen from the top of the unit. You will need a driver extension with the appropriate driver head. I used  four 1" Philips wood screws with washers to support this unit. The cabinet thickness itself is about 1/2 inch, with 5/8 inch flat pieces forming a perimeter around the bottom of the cabinet.
The old unit was directly wired to the electrical through a standard hole in the rear. This hood has the electrical prewired to a 3-prong plug, and the cable exits from the top. This required a channel to be notched into my rear perimeter piece, to accommodate the cable, allowing me to utilize existing opens, within the cabinet. I decided to wire an electrical outlet inside the upper cabinet using a metal surface mount box, and metal receptacle cover. A 6 inch diameter vent elbow will fit over the opening, but not 6" aluminum flex vent. The hood vent is comprised of a 1/2 inch high 6 1/8 inch diameter opening. Inside this is another ring housing two back-flow prevention flaps. I used the standard elbow covering the entire opening, secured by a tight fit and foil tape.