Nitrox(32/36) is best around 25-35m.Just came out of the DN in the Raja Ampat itinerary total of 36 dives of which only 2 below 25 meters
dives were almost all 60 minutes and generally around the 18 meters 60 feet mark
We were the only two diving on air on the boat and we never went anywhere near 10 minutes to the decompression limits
For what concerns fatigue most of the times we were among the last people to go to sleep
I do not see the point of using it if the dive is shallower than 24m. And I could never prove that the gas would make me less fatigue or not even after 4-5 dives a day.