I have at least a half a dozen M12 4.0's - other than in one of the lights or the radio, I can't remember the last time I used one. Using them professionally, the 2.0's give plenty of run time in my Fuel stuff. I just don't care for the added bulk of the XC batteries, nor do I ever find them necessary. Like Mike above, I only run 4.0 or larger in my M18 stuff, so an M12 Fuel tool with a 2.0 is definitely compact in relation. As a pro, I would never sacrifice the power of the Fuel line for something that's just a little bit lighter / more compact.