I used the camera with and without the FOTOS App.
Leica promotes the Leica Photos application as the modern (digital) interface between the smartphone and the camera. With the WIFI enabled on both the camera and the smartphone (an iPhone 5S in my situation) the screen of the phone is a substitute for the monitor display of the regular M10 and M10-P. It is an unpractical solution. Holding the camera in one hand and the phone in the second hand (that is all normal humans have), you cannot focus rapidly. The only practical solution is the fixed distance setting while changing the distance with your arm advancing more or less. This is by the way the classic solution for street photographers who fix the distance setting to exactly 1,75 or 2 meters and change the physical distance between camera and object to focus sharply. The other option is to lay down the phone and handle the camera with both hands. Problem now is that the small screen requires you to position the phone close to your eye. Perhaps with a large screen of more recent smartphones there is more to see.

The best option is to use the camera on tripod and then to activate the app. For photography on the run with dynamic scenery the app is not suitable. Then the classical choice of the view/rangefinder is the best way to operate the camera.
When the app is activated there are a few selections to make in Live Mode: The File Format and Resolution (when using JPG) can be selected as are the metering options (spot, center-weighted and multi-field) and the White balance (hardly ever necessary to select one as the DNG option lets you select the colour balance on the computer.
The camera settings can be found under (obviously) the Settings tab. Here you find most of the menu options that are available to the user of the M10(-P).
The most natural option is to use the camera without the App and rely on the viewfinder. There are a few, but useful indications in the finder area, like number of remaining pictures, the battery capacity and the shutter speed (in A-mode). Also the flash symbols are visible.
The finder is very clear and the bright (white) lines of the frames are well lit. The illumination is by LED's but the frame lines are projected by physical masks. An electronic option would be possible.
Knowing that the camera is digital, gives the initial impulse to look at the monitor after taking a picture. This impulse is soon repressed.
The camera's simplicity and the lack of the monitor have seduced many commentators to apply the designation 'analog' to the handling. This impression is intensified by the little lever that works as a thumb support. As a support there may be improvements possible, because ergonomically the support does not function quite well. You need all fingers of one hand for a firm grip of the camera and after some time, walking around with the thumb behind the lever, the camera starts to slip because of fatigue. Perhaps with more exercise?
The very low shutter noise makes it hard to know when exactly the shutter has been fired. The counter that indicates the number of remaining pictures helps! The classical portrait session when the sitter relaxes after hearing the shutter firing and the photographer quickly shoots another picture to capture the relaxed pose has vanished. It should not be difficult to include an option in future updates to increase the shutter noise.
The general operational features and the performance of the M10-D are similar to the standard m10 and need not to be discussed. The main topic of the M10-D is its analogue feeling.If (and this is a big IF) we assume that the delay between taking and viewing the picture is the defining characteristic of the chemical/physical process than there is some logic in treating the M10-D as the analogue version of the digital camera. But this delay is an illusion. As soon as the smartphone is activated we can see the results. When there is no smartphone, the direct access to the laptop will do the job. The Polaroid effect we do not have: there is always a time lag between taking the picture and looking at the finished picture. The essence of the chemical/physical process is not the immediacy of controlling the result, but the risk factor and the lack of flexibility. First the risk factor. There is always the chance that the picture goes wrong: exposure setting is wrong, chance element is not controlled, unsuitable developer has been selected and so on. The inspection of the film strip after development always produces surprises. The most important negatives are unusable. The digital process on the other hand gives fool-proof results: there is always the software that comes to the rescue.
The lack of flexibility is the second characteristic of the chemical/physical process. Before we start taking pictures, we have to select the film (negative or slide, colour or bw, low speed or high speed). When the selected film is the wrong one, we are lost. In the digital world, even with the M10-D, we can select auto ISO and we gain lots of flexibility. When taking pictures (handheld) with ISO 100 bw film, we may be confronted with low shutter speeds: the choice then is under exposure or blurred images. A change of ISO settings as on the M10-D is impossible when using the M-A. There is a limited option to under expose and use a suitable developer to increase the density but this procedure has other problems.
The basic fact is that the M10-D produces numerical virtual files and the M-A produces (after a lengthy process) fixed physical negatives. The result is different and the process is different.
Claiming that the M10-D invites the user to the analogue world is an illusion. The simple fact that there is no darkroom involved when processing M10-D images says it all. The analogue mentality is absent when using the M10-D. To understand the difference, compare the handling and workflow of the M10-D with the M-A or even M3 from picture taking to the printing stage.
The emphasis on the analogue feeling has obscured the real merits of the M10-D. The operational environment is different from the M10 and previous digital models. The inability to check the result immediately is a fine reminder of the fact that risk and chance are elements to confront in the photographic workflow. The fake transport lever as a thumb rest is evidently a suggestive feature that is unmasked after the first release of the shutter and the immediate motorized tensioning of the springs.