I have used numerous companies' flashes, and I have concluded that what I have been using steadily for the last 10 years, Metz flashes, are the best. I use both 44 MZ-2 and 54 MZ-3 Metz flashes with the Leica module (#5402) on my Bessa R3A with complete success. I simply set the flash to 'automatic' since there is no TTL flash capability. I then set the flash's aperture setting to that which my lens' aperture ring is set for. Following that, I set the flash to agree with the focal length of the lens attached to my R3A as well as the film speed, and I am ready to go.