Consider proportion, balance, aesthetics and function when deciding upon the size of a knob or pull for your kitchen cabinetry. A large cabinet door or drawer needs a larger piece of hardware, or maybe two, for proper functionality, but a smaller size knob or pull is appropriate for a smaller door or drawer. A good rule of thumb for traditional or transitional style pulls is that they should be about one-third of the length of the cabinet drawer. Drawers larger than eighteen inches wide may require more than one pull or knob. However, more contemporary designs call for longer pulls that are at least two-thirds of the length of the drawer or cabinet door.
The cons are a few: 1. MDF is heavy in relation to wood or plywood. 2. MDF does not accept screws very well. You must use coarse thread screws and always pre-drill. Apply the hinge screws by using a hand-held screwdriver instead of a screw gun. If you don't, they can strip the hole quickly. 3. Over time the screws will come lose just from opening and closing the doors (just go around every so often and tighten the screws). 4. If water gets into the doors, they will swell and they will need to be replaced so seal them well.
Generally speaking, I like to see a combination of knobs and handles/pulls. Knobs or handles for the doors and handles or pulls for the drawers. If you are painting your kitchen, the extra holes can be filled, sanded, and smoothed prior to painting so you can start with a clean slate and choose any hardware for your update. I say “generally speaking” because lately I’m drawn to kitchens that have all handles like this “before” photo of a kitchen we recently updated.