Okay, I thought you were interested specifically in that Shockli/Keeppower 5500mah 15A 20A cell that you linked to. It should work well in the MF01 mini, although it won’t give the highest measured output.

If you want a higher drain cell to max out the measured lumens the iJoy 4200mah is a good one.

Looks like most 21700 do fit. Molicel and Samsung make good 21700 cells. If you dont have a spacer, just cut a piece of cardboard to help center it.