Well I use flash, but don't see the need for TTL metering,etc. on a rangefinder. For my nighttime views (see my gallery) sometimes I use a little fill flash, but not sync'd to the camera, It is night, so I have a 1 sec or longer exposure time (camera on tripod, cable release, etc). I just yell at my buddy "FIRE!!" when the shutter is open. Works almost every time.
Besides on some of the old cameras I like to use there is no flash sync.
In the studio, with studio strobes, it doesn't matter what the shutter speed is, as long as it sync's with the flash. Modeling lights are dim in comparison to the output of the strobes.
Never did like on-camera flash.