On an individual basis, flex / reduced power take off's do not save fuel.
Whilst not the most cost efficient profile when taking into account all other factors a full power take off followed by a max continuous thrust climb to altitude will save the most fuel.
This will allow the Aircraft to get to cruise Altitude as soon as possible where it burns the least fuel.
This is my technique when operating at the very limits of my Aircraft's performance on long range operations and has made a noticable difference.