In regards to progressions I believe the following is a good description:
A progression is like a credit card – get what you want now and pay it back with interest later
Flat bet with selective 2 bets at the right time either positive or negative is like cash and cash is king
A 2 bet at the right time is enough to get you through a bump in the road and also enough to maximise your wins
The most successful players on this forum as far as I know seldom go past a 2 unit bet.