A few things have given 'Ultrafire' a bad name for vaping (and flashlights).
I used to use them, a lot. But my vaping requirements have changed and they won't cut the mustard for my current resistance in cartos.
The Ultrafire protected cells I'm familiar with have a protection circuit (that everyone blames on poor Chinese quality control) that senses the current (via voltage drop across the single back to back Mosfet) and trips at about 2 to 2.5 amps. The cell has a fairly high internal resistance and high current isn't it's long suit anyway. The protection board does it's job and trips when you try and draw too much current. They were fine back when I vaped 2.8 ohm cartos at 3.7 volts, but now that I'm vaping 1.5 ohm cartos the Ultrafire doesn't seem to handle that.
Since most protection circuit boards use the same voltage sensing circuit any with a single Mosfet pair (the 8 pin chip) will trip early with a LR carto (or a boost mod).
Circuit boards with 2 Mosfet chips have half the voltage drop so it takes about twice the current across them to trip the protection circuit (about 4 to 5 amps). Hopefully the cell internal resistance is low enough to handle that much current without heating up.
Similarly, a protection circuit board that has 3 of the 8 pin chips (all wired in parallel) will trip at about 8 amps.
If you vape above 2 ohms @ 3.7 volts, or use a buck mod (lower current load on the cells) then just about any protected 18650 will work.
If you need more than that, pick a cell that was designed for it.
Or, you could just blame the Chinese