Crikey! How many different opinions by the chest banging thousands-of-hours brigade! here are my observations for what they are worth......
Changing flap settings during takeoff introduces simulaineous distraction, and change in flying qualities, neither of which are appropriate during a takeoff by a pilot who is new, or new to type.
This is the RECOMMENDED short field technique in my POH. My aircraft only uses "take off flap" though. I agree with the "New" bit though, best practiced on a long runway until competent.
Every PA 28 I have flown used 2 stages (25 deg) of flap as the RECOMMENDED s/f take off technique. Using less and you are not using the RECOMMENDED POH procedure and it won't give you the POH uoted perfomance.
When doing a soft field take of, I hold the stick back and full power - once I have seen airspeed is alive, then I don't look at it again, when the aeroplane wants to fly it will fly. As soon as it is in the air, I lower the nose and fly along the runway a few feet up in ground affect to accelerate before climbing away.
Finally, Ernest K Gann avoided the Taj Mahal in India by selecting full flap after take off. His plane was severely overloaded (unbeknown to him) and wasn't climbing away with the Taj on the nose. Just before "impact" he selected full flap which enabled him to balloon over the TM, before slowly climbing away. So do whatever it takes, if there is a fence at the end of the field, are you going to go full flap or just hit it? I know which I'd do
