Comparison with the Matias Quiet Pro 75%...
The big difference is in the key stability, which is far superior on the Keychron (and the GamaKay I mention below). Matias Alps-style key switches are rather wobbly, at least in their first-run pre-order units made about a decade ago. I don't think I have to explain how distracting that can be. OTOH, simple direct comparison of "naive" key presses still give me the impression that the Matias switches have superior tactility and actuation. The Matias also doesn't have dedicated home/end keys or circus lighting.
Comparison with GamaKay TK75 SOCD...
My partner got a TK75 about a week ago and he loves it. Its about $40 cheaper than my Keychron and uses a silent mechanical (not magnetic) switch called Pegasus. My own impression is the GamaKay switches deliver on their claims better than the Keychron banana switches; not just "better", they are consistently quiet, more tactile and feel a bit better to type on. Key stability is about the same.
More notes:
This Keychron K2 HE appears to be a 'v2' updated version, and I think the big change they made from the first is they reversed the magnetic polarity. The key switches in v1 vs v2 are thus not interchangeable, and from what I gather it is the v2 that matches the polarity of most other hall-effect or TMR boards out there (I may be wrong, but it looks like HE and TMR are using same or similar switches even though the backplane tech is different). I think the only sure way to tell you're getting the updated version is to look for (I kid you not–) "Magnetic Lime Switch" or "Rapid Lime Switch" in the description.
Fun fact: Keychron marketing uses HE and TMR descriptions interchangeably. However, a page on their website says "HE" just means anything magnetic, and actually all their magnetic keyboards use TMR tech. So these "HE" boards are more high tech and performant (and lower power consumption) than their labeling suggests.