The modchip Picofly V1 is 20€ on taobao and the chip Hwfly v6 Oled is 13€.
And it looks like they added an increased current protection chip (to avoid burning the motherboard),
Picofly V1
Hwfly V6 oled
yes it works well with ubuntu, I just tried with a rp2040 zero and I got the firmware "test.u2f" with this command:
sudo picotool save test.uf2
I used this tuto to install picotool correctly:
https://jamesachambers.com/getting-started-guide-raspberry-pi-pico/