I got it second-hand without the keycaps and probably at too high of a price...
The stabs are pretty rattly (some feels like they are stuck somewhere too) and they are not lubed at all. The stabilizers are plate mount only, and the carbon fiber plate cutouts for the stabs are really tight, and I had trouble fitting the durock white stabs into it (only managed to get it in after a lot of force, slightly shaving off the cutout to give it a bit of a chamfer, and the plate shaving off the edges of the stabilizers a bit).
The default keymap doesn't have a DEL key mapped (I think it makes the most sense to map DEL to the top right corner key) and had the least used keys on a 104 mapped to the top right corner. The official driver software doesn't allow remap of the base layer and for "offline mode" (probably means profiles stored on the keyboard) doesn't seem to allow changing the backlight mode for some reason. The software is just overall pretty confusing. There is a command line tool on github pixeltris/GK6X that allows for more customizability, though it's kinda hard to figure out (I still haven't figured it out).
It doesn't have a power switch, and the "optional" keyboard lock with Fn-Tab doesn't seem to be present on the one I got, so the only option for disabling bluetooth seems to be Fn+space to toggle between wired mode and wireless. Though that will be pretty easy to mis-activate if you carry it in your backpack.
The keyboard is also about a cm or so higher than the other ones you mentioned.
There doesn't seem to be any initiative to port QMK to the board.
Right now there are some premium options for 75% namely keychron Q2 and GMMK Pro and I want to try 75% with some space between the alpha region and the direction and nagivation keys too. My quip with those are that GMMK pro have a rotary encoder in place of a key on the top right, while Q2 has only 3 navigation keys under the top right.
Fuling (FL-ESPORTS) has a Q75 with similar layout to GMMK pro with a key at the encoder position but might only be available on taobao, also it has a high gloss polycarbonate case, and probably also proprietary firmware.
Keychron said on a twitter post that they are planning to release an updated revision for K2 with QMK support so maybe wait for that if you are interested. (also there are already a wireless and hotswap version of the K2, though in weak connections they tend to repeat the last letter typed)
