The citrate and bicarbonate forms are much better tolerated, and at much higher doses. I take 3 teaspoons a day of potassium citrate, in water, spread throughout the day (I built up to this over time) because I have a mostly meat and dairy diet. This yields approximately 6 grams of potassium a day. For most people building up to 2 teaspoons a day is sufficient. This much potassium chloride would be dangerous.

The primary symptom of too much of the citrate or bicarbonate forms is diarrhea. Also, the metabolic byproduct of citrate is bicarbonate, which has a far greater effect on body pH than taking bicarbonate itself, as the process increases blood pH rather than that of the intestinal tract.

MK4 is the common one in lots of things. MK7 is the form found in quantity in nattō which is not commonly consumed outside Japan. It can be supplemented.