First, standard MX style switches are either 3 or 5-pin:
The big round plastic part in the center is counted as a stabilizing pin. The 3-pin switch has the middle plastic pin and two metal pins. A 5-pin switch is the same as a 3-pin, but with two extra plastic stabilizer pins on the outer edges. With a standard 5-pin switch, you can clip off the little outer plastic pins and fit them into a 3-pin socket with no problem. The UHK will accept both 3 and 5-pins though. No need to clip the stabilizers.
There’s a zillion switches & caps out there, so we can’t feasibly go through em all.
The Kailh Choc V2 switches for example, have a 4-pin layout, and I think the center pin is bigger, so they don’t fit a standard MX socket:
I’ve seen those Shadow Series switches before, but I thought they were just a new Kailh Choc V2 variant, which again, aren’t compatible with standard MX sockets. BUT… after looking at the video on Kailh’s site, the Shadows do have a 3-pin layout that at least seems like it could fit standard MX. The product compatibility info also says- “Works with any PCB compatible with Cherry style switches. 5 pins can be modified to 3 pins by clipping off the extra 2 pins if necessary.” Then if you scroll down the page, you’ll see a “Switch Replacement Guide - Adaptation Instructions” showing what looks like the layout for normal 3-5 pin sockets:
EDIT:
After looking closer at the Shadow Series, it appears they are NOT compatible with standard MX sockets. The two metal pins are aligned in a more rightward position compared to the MX switches. The center plastic stabilizer pin also has a wider diameter than the MX’s.
Now, I’ve also heard that low profile switches might not fit because the thickness of the plate above the PCB can be too tall for the switch. I’m also not familiar with Lofree keyboards, which is what it looks like those switches are designed for. Looks like they’re a KAILH*LOFREE collab, so it might be a unique format.
As for the “weird thing connected to the pin”… If you mean the black thing in the second image you posted; that looks like a Kailh low profile hot swap socket adapter.
So, IDK for sure, but I guess it’s probably worth looking into the Shadow Series switches further. I’d honestly try to contact Kailh directly and get confirmation of their compatibility with standard Cherry MX hot swaps if I were you.
As for keycap compatibility, just make sure the stem on the caps are the same MX “+” shape as the switch. Normal height caps will not fit low profile switches without hitting the plate or getting stuck on the switch’s plastic housing. I assume most low profile caps should work with normal MX switches, but they might expose a bit more LED under-shine than you’d like.
Fortunately, finding customizable low profile caps for MX style stems is possible here:
Just choose the “LPF” cap style, and there’s a template for the UHK layout. If I’m not mistaken, I think their LPF caps are a uniform height.
I have some of their XDA profile caps which are taller than LPF, but a flat uniform height:
If you join FK Custom’s Discord, they’re really active & helpful on there if you wanna ask questions about their caps.