Check the hidden work
Ask the cassette bidder to show the available ceiling space, mounting method, finished opening, refrigerant route, drain route, and service access. Have them explain whether joists, insulation, wiring, plumbing, or other existing features affect the location. Any structural or electrical work should have a qualified provider and a named owner in the quote.
A manufacturer's instructions make these details concrete. Mitsubishi's SLZ-KA09/12/15NA cassette manual addresses ceiling support, maintenance space, a drain pump, and an installation drainage test. Those requirements apply to those named models; your proposed cassette needs its own installation instructions. Mitsubishi cassette installation manual, RG79Y612H02.
For a pumped drain, ask which pump is included, where a technician can reach it, what happens if it fails, and how a water problem would be detected. Request a drawing of the drain destination and confirmation that the installer will test the completed route. Do not accept a hidden drain route that nobody has checked simply because the ceiling finish looks good.
Compare daily use and future repairs
Ask to see how you will clean the normal filters. Consider whether you can do that comfortably and safely in this room. Ask how a technician would reach the fan, coil, drain components, and electrical compartment. If repair means cutting finished surfaces, get that limitation and restoration responsibility in writing.
Then compare airflow at the bed, couch, or desk, the controls, the quoted noise information, and the complete installed price. Check the exact warranty and local service support for each option. We would give more weight to a well-explained installation than to an unsupported claim that one style “never leaks” or “always fails.”
Your next step: Request the cassette model's installation drawing and service-access plan alongside a wall-head alternative. Choose the option whose comfort, appearance, care, and repair needs all work for your household.