Here is a quick image comparison between the Leica SL and the Leica M 240 with the Summilux M 35mm FLE.
As you can see, the Leica M produces much warmer colors and a bit more vignetting. I prefer the Leica SL as the images look more natural. Of course I could correct the white-balance to let the M240 images look like the SL-images. But I have to do that every time for each picture. Sometimes the M240 toning is attractive even if it is not neutral. At the end it’s a matter of taste.
And here is a comparison between the Leica SL with the Summilux 35mm at f4,0 and the native lens 24-90mm with 35mm and at f4,0.