This ain't rocket science.
Modified sign wave; Depends on how close to pure sign wave it gets. Cheaper usually means not so close. This will cause some electronics
to fail outright ( may not ruin them but they just won't work ) and ALL electric
motors to eventually fail. ( if they are one of the cheap
Simple test. run your drill/fan/aircon/shopvac whatever, on shore power
and listen to the sound it makes.
it into a "Cheap" modified sign wave and listen.
You can HEAR it grinding your electric motor
Only a matter of time, and your money