BTW, if I'm not mistaken, Adafruit's bootloader ( https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/update-bootloader ) should work on these dongle boards as well. I suspect the way it may works is:
0. Install the booloader as per the instructions in the link above. Thereafter,

1. Plug the dongle into the usb port on your pc, whereupon lit's treated like a virtual hard drive.
2. Drag the binary you want to upload to the virtual drive icon on the PC
3. Reboot to finish, and that launches your program.

Anyone tried it? If so, is that a correct summation?

As you can see, the one in the left side, is holding by itself, it does not has the cables soldered though, the one on the right is my first iteration, but the side holders are weak and broke with time.
It is true that the fact of picking the two side points, it makes it self aligning.
The blue versions are the newer ones, where you can slide it in with the pogo pins stretched out, and then you press it in and lock the open space in the bottom with that small blue little thingie that we see unused and free in the middle version. So no rubber band required, all is static mechanics.
Both middle and left versions are available, the middle version requires glue to fix the pogo pins in the printed shell after being inserted the first time but makes soldering the wires on top easier. The left one has a roof holding the pogo pins but they're harder to access for soldering the debug wires in them and also printing is with slightly more debris given the complex bridging.
One way or the other, this managed to get me a self-standing pogo pin adapter of an already existing board. Indeed if you design your own, you can think of those you linked, but if you're short of space, you can also fallback on such custom 3d printed solutions.
This nRF52840 usb dongle is an amazingly powerful board and so cheap, that I'm confused why Nordic did not made the debug for it simpler, feels like they prefer to sell the dev kit for prototyping, but they don't know how hobbyist like to prototype on the final cheap product. I could afford 5 of them to experiment with some mesh protocols.

So if you have access to 3d printing and would like to give it a try, I'll stay around and help if needed, also if you have improvement suggestions, I struggle with fusion360 till I get things done.

I've been kinda intriqued by these things: https://www.segger.com/products/debug-probes/j-link/accessories/adapters/10-pin-needle-adapter/
because it's general purpose and you can lock them on, but the downside is that the latching holes consume a fair amount of board real estate.

I also like platformio Arduino and would like to have the nRF52840 USB dongle supported without the softdevices, as they prevent the direct usage of the RF peripheral for custom radio.

static void pa_lna_assist(uint32_t gpio_pa_pin, uint32_t gpio_lna_pin)
{
    ret_code_t err_code;

    static const uint32_t gpio_toggle_ch = 0;
    static const uint32_t ppi_set_ch = 0;
    static const uint32_t ppi_clr_ch = 1;
    
    // Configure SoftDevice PA/LNA assist
    ble_opt_t opt;
    memset(&opt, 0, sizeof(ble_opt_t));
    // Common PA/LNA config
    opt.common_opt.pa_lna.gpiote_ch_id  = gpio_toggle_ch;        // GPIOTE channel
    opt.common_opt.pa_lna.ppi_ch_id_clr = ppi_clr_ch;            // PPI channel for pin clearing
    opt.common_opt.pa_lna.ppi_ch_id_set = ppi_set_ch;            // PPI channel for pin setting
    // PA config
    opt.common_opt.pa_lna.pa_cfg.active_high = 1;                // Set the pin to be active high
    opt.common_opt.pa_lna.pa_cfg.enable      = 1;                // Enable toggling
    opt.common_opt.pa_lna.pa_cfg.gpio_pin    = gpio_pa_pin;      // The GPIO pin to toggle
  
    // LNA config
    opt.common_opt.pa_lna.lna_cfg.active_high  = 1;              // Set the pin to be active high
    opt.common_opt.pa_lna.lna_cfg.enable       = 1;              // Enable toggling
    opt.common_opt.pa_lna.lna_cfg.gpio_pin     = gpio_lna_pin;   // The GPIO pin to toggle

    err_code = sd_ble_opt_set(BLE_COMMON_OPT_PA_LNA, &opt);
    
}

in this form i like the ble, without pa not so much. theres just big down side which is nrf52840 definitely not hobbyist friendly. next time i may design a quick nrf52832 pa board (this one has regular QFN package) to test with the same setup and compare the results.

then i uploaded the adafruit feather bootloader to test the bluetooth and it all works ok. i used my iphone 6s as a central device and im not sure if my phone has LNA or PA module inside for bluetooth so it may or may not be better if i use another module like the one i did. this connection is from my module to my phone WITHOUT PA activated at tx power max(8):

and this is after i activate PA chip on board :

and this is with 3 solid walls in between at around 10 meters distance

as you can see signal strength is massively different pa bumps up the signal from -87dbm to -30dbm which is probably day and night difference.
but with this setup you manually have to enable and disable rx and tx pins in order to keep the communication. well im not really good at coding but im going to try make the whole thing automatically because nordic already has this PA assist feature buried inside its BLE core, just gotta find a way to make it work.

final board, forgot to add i opted to use pcb antenna but i could switch to external antenna as well i just have to reposition the 0 ohm resistor to use that SMA on the side and then results could get even better:

yes this is possible with nrf52840, but unfortunately zigbee is not compatible with mysensors. Mysensors is a software stack like zigbee is.

I think you'll get more infos if you take a look on nordic semi forums. They have a zigbee stack for nrf52840.

However, I presume the better way would be to apply solder paste on the pads before sticking on the module and then reflow it in an oven.

It has some improvements, but some of its competition seems to be much lower power.

@NeverDie Ya Adafruit's Clue looks great. I just wish they would have added one more button to the front so up/down/select could be used for a menu system on the display.

Maybe you could program one of pads #0, #1, or #2 to be a capacitive touch equivalent of the extra button you wish it had?

The listing says it's programmable from the Arduino IDE.

The original micro:bit seems locked in time, with no official mcu upgrades from micro:bit itself, but nonetheless by the end of 2018 over two million micro:bits had been distributed globally. Pretty amazing for such a minimalist, barebones platform.

My impression was that the snow coating acted like a mirror thus greatly extending the range. But I admit 14 km is ridiculous. So sounds like a challenge :-)