I do, sometimes ... Metz 54 Mz 4i on the M7 ... still waiting for the SCA-3502 to be able to use high speed synchronization (HSS) which I think is a good feature, and I think the 2nd shutter curtain sync flash (which I really don't use much even with my dslr so not much of a concern for me) ... also have other smaller flashes, but only for 1/50. Erwin Puts did like the fact that HSS can be attained with the M7 using the Metz 54 M3 (I don't think they make this anymore), the MZ4i is the new flagship.
Would have liked the Leica flash, but it can't even swivel the head, not for serious flash use (Leica must have been thinking it's users don't use flash or don't know how to use it). Only thing I can find it useful for, while maintaining a relatively quality flash shot, is for fill flash outdoors.
Here is a clearer explanation of the 2nd curtain sync flash, courtesy of Canon
(Nikon's SB800 flash user manual has the same explanation) :
http://web.canon.jp/Imaging/flashwork/functions/curtain/index.html
On my Metz, there is a function for "Rear", there should be one too on the SF24D, if it supports rear flash sync. Then, the M7 has to be activated (press shutter halfway until you see exposure settings) ...
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