I'm struggling to make a decision to change my M10 for the SL2 or 2s. I would be using my M lenses primarily but would hope to buy the L fit Sigma 40mm 1.4 Art as an af lens. I have no interest in video and the only reason I want to change from the M10 is that I'm getting older and even with the +2 diopter and the Visoflex it's becoming a bit of a strain to focus. I have the 50mm Summilux ASPH, Zeiss 50 1.5 Sonnar and Zeiss 25 2.8 Biogon, also a Voigtlander 35mm 1.2 II ASPH. My worry is that the SL cameras will not give me the same files as my M10. Will I notice a difference? Thank you.
TL;DR: The SL2 system is better technically (if using SL glass), but I generally prefer the images and shooting experience of M system to SL2. Evaluate for yourself before switching, and don't rely on reviews. The two systems couldn't be more different.
I have both systems. Unless money is a factor, I highly recommend you get the SL2 and live with it for a while before swapping systems. I'm only saying this because, as you're likely aware, the shooting experience couldn't be more different between these two systems. IMHO, the SL system only shines relative to the M if using SL glass, for the optics and if AF is needed. That said, SL2/s AF performance is not on the same level as what you get from the big three, so set your expectations accordingly if AF is the reason for switching -- but perfectly sufficient for anything non-action oriented.
In terms of files, it naturally depends on if thinking M10 or M10R (ruling out M10M since evaluating vis-a-vis SL2/s). Using the same glass (m lens adapted to SL2) so camera is only variable, the differences between SLS2 and M10R are subtle enough that I suggest you not let "the files" be a dominant factor in your decision making. The M10 sensor is older, non-BSI type, so if you stress the files in LR or C1, you're going to see the SL files hold up better, but, frankly, the M10 files are still very good and I still wouldn't let it be a factor. If you're needing the AF, then it is a much more compelling reason to switch. Putting M lenses on the SL2 works, but peaking is not a very reliable way to nail focus and I find using M10 focus patch over peaking to be better and faster, and using magnify is also slow, so if moving to SL for AF, then best to mount AF lenses and use the AF.
Regarding the SL system, it's a system I struggle with decision to keep or not. In terms of design and build quality, it's an easy camera to love, and the shooting experience, for me, is second only to M, but I don't find myself using the SL2 very often (lately, mainly for mounting to Actus since I have an L-mount camera adapter). The problem is, the number of times of reach for M vs SL camera is about 10:1. the M is more portable and, as indicated, I prefer the shooting experience of M to SL. Also, while highly subjective, I generally prefer the images I get from M system over SL. It doesn't make sense on paper, and perhaps because M forces me to slow down more, or maybe possibly because I'm biased towards using it more often and therefore have more experience with it, or both. IMO, the main benefit of SL is the AF and IBIS (esp. as compared to M10R). My challenge w/ the SL2 is I'm an MF shooter first and only use AF when absolutely necessary, such as sports/action, and in this regard there are much better options available outside of the Leica ecosystem. Hence, I don't use SL for sport/action either.
Of course all the above is my opinion, which is all you'll find on forums. The only opinion that counts is yours so take in all the inputs, but, again, I highly recommend you to try (for a while) before pulling the trigger on switching from M to SL2 because they're apples and oranges systems. The SL (601) is also a very nice option, esp. if you don't care about video, and used ones in excellent condition are readily available for a fraction of the cost of SL2, and even include build-in GPS, which is a nice perk. It's great camera to get some seat time w/ the SL system if thinking about an SL2, and if don't need the resolution of SL2 or more video-centric SL2s, you may find SL (601) is right for you.