The really nice thing about them is that they accept 3v3 logic when being powered by 5v. Although that usually works with the WK6812, it's technically out of spec and I have read about this causing stability issues. They are also pretty low power, 12mA at max brightness (these are at 1/32).
They are reverse-mount, so you don't have to be concerned about keycaps colliding with LEDs.
Firmware is still definitely a WIP, as is the motherboard (the keyboards are i2c daughter boards as per my previous post). I have switched to embassy-rs, which is way more ergonomic than embedded-hal - async rust makes tons of sense for embedded dev. I'm also going to be printing blank shields for the RPi Picos, to hide that green a little better.
If you've been putting off designing your own keeb, I strongly recommend it. It's really rewarding.
Usually, logic levels are not a big issue, just saying. You have 5v anyways, all you need for a unidirectional level shifter for low baud rates is a mosfet and a resistor.