LD-2 M2 4S 25mm dia. Linear driver I thermal epoxied AS5 the driver directly to the head, with a dab of AS5 grease in the middle and drilled a whole thru the pcb for spring to LED + and the mcu + feed, off a pad on the stripped pcb . The LD-2 M2 driver utilizes the tail cap and e-switch for mode changes. It would seem an LDO would be needed, never looked into it that far. It switches great off the tail cap and e-switch with no issues I have seen so far, and I’m running them on 2 of the same type lights …I like them, just more work since they don’t support a pcb in which to mount a spring, like a regular driver, you have to become a little more adaptable, and innovative in the placement of them, they do get hot so heat sinking is with out saying right so I removed the ano inside the head. Need a smoth reflector now? 
LD-2 M2 thread… Discontinued: LD-M2 - info and FAQ thread (up to 19V 20Amps PWM-less linear driver)