A whole lot was changed to cheapen the Model F and create the Model M. Two-thirds of the costs of the Model F were cut to make the Model M.
The Model M made some sacrifices on build quality and tactile response, replacing almost all metal with plastic. Out was the incredibly sharp and firm click of the Model F’s flippers making direct contact with its large printed circuit board. In was the Model M’s tiny pivot plates hitting a rubber mat and underlying plastic membrane sheets with a relatively dull thud.
The Model F is definitely the gold standard of buckling spring keyboards.