That's like asking, "How much better is Osmocote than Miracle Gro?" - they are too different to really compare. I am only saying that from looking at the ingredients, I have never used PMDD, I just know it is popular and effective, if a bit more fussy than just liquid dosing. Here are the ingredients side by side so you (and anyone else reading) can see the difference:
Leaf Zone
Soluble potash (K20) 3.00%, Iron (Fe) 0.10%, Chelated Iron (Fe) 0.10%. Derived from: Potassium sulfate and iron EDTA.
PMDD is composed of equal parts of potassium nitrate, potassium sulfate, CSM, magnesium sulfate. CSM is composed of 1.50% total magnesium, .10% copper, 7.00% iron, 2.00% manganese, 0.06% molybdenum, 0.40% zinc.