I wanted flash capability for my M240 but I did not want to spend $630 for the Leica SF58 flash. I found a way around that - the Phottix Ares wireless flash trigger set:
http://www.adorama.com/PH89230.htmlThis trigger set has a range of 200+ meters, according to Phottix. It has eight seperate frequency channels, so you can work in proximity to other photographers using wireless flash and not trigger each other's flashes due to frequency overlap.
Both transmitter and receiver operate using two 1.5v AA batteries, making the units safe for the M240 and your flash.
I talked to the tech guys at Leica NJ about using non-Leica flash units with the M240. Their answer was that current backflow from the flash unit - if it were to happen for some reason - would not damage the M240, as it is rated to 230 volts.
No AA battery powered flash unit or wireless trigger set comes anywhere near 230 volts; since the M240 is rated to 230 volts, it will be safe from any malfunction of the flash or wireless trigger set. I have put my M240, Ares trigger set and my admittedly ancient Nikon SB25 flash unit to the test. All three passed with flying colors.
Why would you want to use flash with the M240, which has a maximum ISO setting of 6400? In a word, image quality. You will be able to use a lower ISO in virtual darkness when using flash, giving you higher quality DNG files to work with, as well as even, uniform lighting, especially if you go off camera and use a diffuser for direct flash or use bounce flash when indoors. A normal height home ceiling will give you soft illumination; bouncing the flash costs only one stop of illumination.
Off camera flash with the Ares trigger kit is something well worth exploring with the M240. It gives you one more option and many more choices for low (or NO) light photography. If you give it a try, you won't be disappointed.