In general there are 5 different styles of range hoods. Regular (undercabinet) and microwave hoods designed for regular ranges. Pro hoods tend to be larger and deeper for professional and commercial style cooking. Downdrafts are for island installations.
A custom insert is number 5 and consists of the interior filters, switches and lights of a hood. The blower can be installed within the insert or located in an external location. The hood can now become a focal point of your kitchen rather than a large piece of stainless steel mounted on the wall. The most common method of covering an insert is wood cabinetry and is more custom looking than any of the other options.