Fenix PD36R with ALF-18

The user manual and product page for the Fenix PD36R both say it can only use 21700 batteries. However Fenix also sell this:

Which just says that it converts a 18650 battery to 21700 size. I’ve also heard someone mention that you can also use 2xCR123 cells with it.

Anyone know if this will work with a PD36R? I don’t want to damage the light. If I had to guess I’d say the 18650 will probably work but obviously with reduced runtime, not sure about 2xCR123 though as that would be 6V which might be bad.