I've seen others do that - buy a threaded mount adapter (LTM -> M adapter) for each lens - to get all their lenses to M mount; might make sense if one had a mix of LTM / M mount lenses.
If you did go this route, one advantage would be you could purchase a single M -> E mount adapter and quickly mount any of your lenses. I really like the Hawk M-NEX (available from the maker off eBay) adapter as it includes an internal helicoid which allows you to close focus with your adapted rangefinder lenses.
For example, the minimum focus distance for my ZM 25/2.8 is 0.5m. Here's an example shot of my kid's messy desk, helicoid collapsed (normal):
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With the helicoid extended fully, the MFD drops to about three or four finger widths from the front of the lens to the subject -- say about 6cm or so. That's quite an improvement from 0.5 meters, all the way down to 0.06 meters!
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This makes any M (or adapted LTM -> M) lens just that more useful. I leave my Hawk's mounted on the NEX-5N all the time except when using a native E mount lens. The Hawk adapter is ~ 179 if I recall correctly.
A ZM 35/2 mounted on the Hawk adapter, collapsed, is on the right, compared to a static Contax/Yahsica adapter with a 50/2 Yashica kit lens of the day.
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Expanded:
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It is well built. The helicoid ring does not accidentally turn while focussing the M lens. You can actually focus using the helicoid if you wish - the movement is smooth enough and sometimes I do this.
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My copy is accurate with my lens's infinity stops and I've not read any other Hawk user having problems with infinity. Some M-NEX adapter (and indeed ??-NEX adapters in general) have problems with this, often allowing focus past infinity, probably "to be safe".