Also, it will only eat unprotected cells. Protected cells are too long.
I think there is some variability in different samples of the QSL working with different length batteries. I found that +\- ~0.5mm can make a difference in whether the [cell + plunger] length is too long to allow the tailcap to be tightened down, or (on the other extreme) whether the [cell + plunger] length is too short to reach the switch in the head.
I wanted to use protected RCR123, so I shortened the length of the plunger slightly using some sandpaper. The price is I can't use primary CR123 with that tailcap any more.