What it takes for one to become proficient at focusing with a Leica M is:
- that the lens and rangefinder are properly calibrated. (This is usually the case ... unless you bang your equipment around a lot, the Leica M rangefinder is pretty robust and durable; it does not ordinarily just "go out of calibration" unless the camera is banged or dropped pretty hard.)
- that the user practices focusing until it comes as second nature. (It's not difficult, but it does take both a good feel for the lens' focusing ring and the visual appropriation of when the RF image coalesces together. If you read the Leica M instruction manual and follow the instructions for use, and then practice, it comes pretty quickly and easily for most people.)
And then, how the M (whether film or digital) differs from a 100% view SLR, DSLR, or mirrorless EVF camera is that the optical system's rangefinder framing lines are *always* approximate. And lens focal lengths are, again, *always* approximate. So what happens is that, with continued practice and use, you get to know your camera and lenses intimately and use the RF framing lines as they are intended to be: as close approximations of what you're going to capture. Once you have learned your camera and lenses, and how they work with one another, you begin to find that you mostly ignore the frame lines because you KNOW what the lens is going see.
It is at that point that using a Leica M becomes fast and intuitive in the hand ... You stop thinking about focus, you stop thinking about the frame lines, you just do it and it is just natural and quick.
The digital Ms (typ 240, M10, M11) have, additionally, the easy capability to use Live View either with the LCD or the optional EVF. This extends the versatility of the basic camera because you can use them for SLR-like/EVF-like camera TTL focusing and framing ... but this capability should be considered definitely an extension of the basic camera functionality rather than the primary way to use it.
If that kind of framing and focusing accuracy is what you're after, buy a DSLR or mirrorless camera. When you do that, just accept that for such cameras (with the Leica models being an exception) that the Leica M lenses are not really best computed for that use. I had several different mirrorless cameras prior to returning to Leica M bodies (Sony, Olympus, Panasonic) and while the Leica M lenses worked "okay" with them, they have always returned superior results for me when used on an Leica M body. Leica R lenses worked much better on the Sony A7 series body, and also on the Olympus and Panasonic bodies... I haven't used the Nikon and Canon mirrorless cameras thus far, but I suspect it is similar for them.
G