First & foremost we would like to thank you @sandra for writing such an extensive review.
I will do my best to explain a few things that might be unclear after reading your article, however, it appears that you might not have done the first update, as you didn’t use the Mudita Center app for some of the features. We had recently released a new OS version (1.1.5 to be precise) that addressed a lot of bugs and errors found during the internal tests, including fixing the audio quality, which might be the biggest concern.
Now, let’s address some of the concerns you raised in your review (I’ll focus on MuditaOS things as that’s what I know the best 
):
Currently, the center key usually means “do it to it”. It’s what you click to go to whatever’s under the cursor in the app menu, for example. When there are two things, “do a small thing to this specific widget” and “finalize the entire thing, the message, the contact, the setting”, the center key is the big thing and the left context key is the small, local thing. In my opinion, that’s backwards. Instead, I would’ve wanted the center key to be the small, local thing and the left context key to be the big thing.
You are right that the center button might be confusing at first, especially when you are used to a more classic approach. There were quite a few design decisions that pointed us in this direction - the most important one was following the rule of “non-distraction phone” - while we were heavily in the R&D phase of the general UX approach, this pattern was proven to have the least needed artifacts on the screen and the best consistency and usability.
There is an autolock setting, deep in the settings menu hierarchy, where you can set an autolock time from fifteen seconds up to twenty minutes, but you can’t turn off autolock. To lock it manually, this isn’t obvious at all, but the way you do it is by holding the # key (when you’re not in a text input field). I usually don’t want autolock on when I’m at home but I usually do want the phone to be locked while it’s in my purse.
True, there is no such option. The design decision here results from our concern for security, however, we don’t rule out changing it in coming patches. We will gladly look into it, thanks for pointing it out!
The speaker, for ring tones and SMS tones, is awful and most of the ring tones and text tones are very clipped and distorted because of that. During phone calls, sound quality is horrible for both me and for the other person. Easily the worst feature of the phone. It comes out of the box crankes up to the highest volume, and, like most speakers, sounds a little bit better and less clippy if you lower the volume a bit. But then it’s too quiet.
As I mentioned - the audio quality should be greatly improved in 1.1.5. We are constantly trying to catch all of the flaws and drawbacks during internal tests, and having community responses in our heads, we are prioritizing the most crucial problems on our roadmap. That said - as you are a quite active contributor, you can create an issue with the audio quality - it should speed up possible R&D.
You can’t have contact-specific tones.
That’s a brilliant idea - don’t hesitate to throw it on GitHub as a request - I think our team will take a look at it.
The main menu is a 3 by 3 grid of icons; on some similar phones I’ve then also been able to hit the corresponding number key to open that app. Not here. That would’ve been especially good in low-vision situations.
This sounds like a great idea - we’ll see how quickly we would be able to implement it.
You can’t set the meditation timer to my usual 20 minutes. 15 or 30 or 60 or 90 only. It also doesn’t save your meditation settings, I need to turn off “chime every 2 minutes” every time. You can turn off the meditation prematurely by hitting the right context key, labeled “stop”.
As I talked with our QA engineers, they confirmed that it is possible to set the timer to 20 minutes. I’ve also tested it and it works - you just have to write the desired interval using the keypad.
I can’t change the text message templates (“I’ll call you in five minutes” and such) on the device itself.
As you already noticed, it is possible by using the Mudita Center app. I’ll find out if it’s intentional to be able to edit those only using a PC app or are there any plans to allow it on the phone. To be honest, I think that sooner or later it will be implemented in the OS 
It comes with a handful of Nick Lewis songs (the headphone speakers sound OK) but those aren’t tagged with metadata (either that or, the song browser doesn’t work properly; the songs only show up under “all songs”).
Grouping the file tags in the music player is under development, so it should be fixed in the next updates Grayed-out options were intentionally left as a teaser
I miss incoming text messages while listening to music or when I’m on a call.
Audio mixing is actually in the research stage, but you can get the notification during audio playback/calls via a vibration. As you disabled it, you’ve lost the notification - definitely a big thing to consider - we’ll take a look at this and see what’s possible.
Sometimes text is truncated (for example, but not limited to, in the message templates) and I don’t know how to scroll it.
Did you try to use up/down buttons around the center button? I had no problems with scrolling the larger blocks of text (such as EULA), although it might be an issue in particular cases. We’re working on it.
And a quick responses to your summaries:
Love that I can turn of the backlight completely
<3
Can’t edit message templates
This will be available in the future for sure
Can’t go back to main screen easily
You actually can! Just press and hold the back button (the right one) - you should be able to go to the desktop within one click.
Can’t tether to tablets
That’s a topic for another thread - It’s related more to the target device’s drivers than to our Phone as we make a passthrough in the tethering mode.
Can’t use USB C headphones, only 3.5”
It is actually a business decision - we have a headphone Jack on purpose as it will give you an advantage of using the built-in audio codec.
Clunky meditation timer
Please be so kind to address it as specific as you are able to. I.e. if you have issues with how the screen looks like - one look is worth thousands of words.
Messed up context / center button semantics
Could you elaborate on this in detail? Or is it just the button assignment issue?
Bad for low-vision users
Tiny, unreadable font
We’re looking into this
Can’t send hearts♥ (there’s a handful of supported emoji)—I hope that a custom template will - solve this issue!
This will be fixed for sure
Can only do European / Latin text (with diacritics), no RTL, no CJK, no other scripts
That’s on our roadmap too.
Easy to miss incoming messages while calling or listening to music
If you have your vibrations disabled - yes. But this also will be fixed.
I hope that I addressed the most important topics. If not - don’t hesitate to ask, I’m here to respond to all your questions. And thank you once again for your review - we’re happy that you like your new daily driver, even if it does not fulfill all of your expectations.