Depends on your service area.
In metropolitan areas the HVAC set-up can vary widely. . Possibly causing the need for a portable unit.
If the HVAC is in the garage a TM unit would be very efficient.
The realty that I discovered is that if the owner replaces the furnace filter twice a year with a high quality filter the system is basically self cleaning.
In your area I believe the big player is the "Air Duct King".
One year I invested 10k in a TM quality Air Duct system. Then The City said I couldn't run the 8 inch hose over the sidewalk, a necessity for most homes in San Francisco