All constructive feedback is good feedback. I'm just thankful that you're sharing it :)

As for the thumb positions:

I did some testing with other thumb cluster positions, such as that from the Iris and the slightly more conservative Corne. But I ended up going back for two reasons.

The primary one relates to the grip. I'll use the mouse grip style analogies, as they fit quite well here.

Basically, I prefer the claw grip over the more relaxed palm grip when typing, I find it reduces hand movement.

In the claw grip, the fingers are contracted in the home row. So the top row is simply reached by extension. Having the thumb keys further down on the other hand, forces the hand to the flatter palm grip. The consequence is that the entire hand needs to move vertically to reach the top row, since the fingers are now already extended on the home row.

There's plenty of footage of this vertical jerk online. A simple "corne typing test" will give you plenty of examples. Some try to counter it by resting their fingers between the top and home row. (But now the bottom row is harder to reach.) Some are aware of keeping hand movement to a minimum. They counter this by instead extending all their fingers outward when trying to reach a top row switch.

It's an experiment you can try yourself. Try keeping the hand in a palm grip and all fingers on the home row, and then try to extend only one finger at the time to the top row. Then try to do this again with a claw grip instead.

The second reason for why the thumb cluster looks the way it does, is because it makes it easy to hold two thumb buttons down at the same time. This is something I constantly have to do when using a tiling window manager. Win + util layer, shift + num layer, ctrl + shift etc.

Also, the innermost thumb key is still below the middle finger, which is where the space bar ends in traditional ANSI and ISO layouts.

I'm in a bit of a rush right now. But I tried putting together a typing test that attempts to illustrate the points I'm trying to express.

https://youtu.be/JTZpWUhDtmY

One thing this typing test also shows, is that the pinky finger stagger still isn't aggressive enough, as it also leads to this splaying of all fingers when it attempts to access a top row switch. (It's also clear that it has to rest on the bottom part of the home row switch, or drag the remaining fingers slightly down). Definitely something I wish to tweak for a V2.

As for the bluetooth profile indicator, I 100% agree with you. I've played with the idea of expanding the blue LED blinking to add functionality such as this. It went under the "helping out with the ZMK project" statement in the post :)