Output will be reduced with a primary, but runtime longer than a R123. Maybe an hour of diminishing brightness(?). It should still be very usable in low light. It'll only take you a minute to swap heads and see if it's suitable for your personal use.
btw, I didn't complete my thoughts before. I think they may all run in regulation with a R123, but the runtime will vary with Vf(some people got less than 20 min. while I think I got about 30).
I put that KL4 on a E2e body, and used it with a protected 17670 Li-ion most of the time that I had it.