being from Meritline i HIGHLY doubt that this flashlight is actually 1000 lumens
In general most flashlights are overrated to a certain extent. 18650's are pretty standard for this type of flashlight, it's the only way to get enough power to the LED, they charge up at 4.2 volts and an AA or even a C or D cell is only going to be at 1.5 volts and it can't handle the current draw on these things. Plus a C or D cell is going to be much bulkier than an 18650.
As for the red trustfires, I've got those but like the unregulated ones better, once power starts to go on them, it goes from super bright to nothing and you're in the dark. At least with unregulated ones, it starts to dim and you know you've only got a few minutes left until it gets really dim and you risk discharging the battery too much.