T-Bone, Welcome to CPF!
Downboy, BadBoy, NextGen, Shark, Fatman nFlex, MaxFlex.
Are all pretty much constant current regulators. Whether they are buck (lower) or boost (raise). As for EXACTLY how they function you need to look into the data sheet.
Your resistor does not control the current and as the battery capacity drains so will the output of your light. Resistor "typically" is less efficient. The only time when they are more efficient is when you put a really really REALLY small resistor in the chain which kinda defeat their purpose.