The MDA is just that - a minimum. If you fly the constant descent profile in a very heavy aircraft, say a 747, you will bust the minima if you TOGA at MDA. For that reason, my the Jepp plates my company uses all have an extra 50' added to the NPA MDAs.
I used to fly with BEagle (in fact checking my logbook, he did 5 of my 6 IRs on that aircraft!) The company policy then was to descend slightly below the notional 3 degree GP and level off to make the MAP at the MDA (legal on all NPAs except SRAs which have lower minima based on the notional 3 degree GP). This is fine if the aircraft can do it, and you stay in currency on that type of approach - we used to have hours allocated for currency training on the aircraft (not the Sim) and had to do one of these approaches every two months. But now I'm flying a much heavier aircraft and rarely flying NPAs - the constant descent and a 50 ft buffer make good sense.