They click, making it sound as if you type hardcore assembler code at all times. Some even click twice per keystroke, which means you have a black hoodie on, even if you are just in your pajamas.
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Ordered one from Amazon for 40€ once, chinese blue switches, brand was Aukey, it wasn't as cool as a Model M, but it had some nifty color effects. The keyboard was ok, but loud when you have video conferences all the time.
what is the advantage of those things? I watched some videos on Youtube a while ago but failed to understand the concept
I'm old enough to have experience with mech keyboards all the way back to IBM Selectric typewriter keyboards, which were considered the ergonomic SOTA for intensive typists. (They used to have these employees called "secretaries" back in the day.) Later came IBM PC keyboards, which weren't exactly the same, but were much more ergonomic than most (actually ALL) PC keyboards in the following couple of decades.
The point is that if you type a lot on typical modern laptop keyboards, there is limited key travel and a lot of repetitive impact on joints and finger-tips. Maybe ok for email and occasional typing, but a problem for some people doing high-vol typing. (It was a problem for me.) By contrast, when you get used to typing correctly on a mechanical keyboard, the long-throw key-press can limit or even eliminate the impact of each key press. The haptics and/or key-click of the different types of mechanical keys provide a physical point of feedback where each key-press can be truncated without much bottoming-out, or in some cases, any bottoming out at all. Takes a little practice to get good at it, but not that much. The original Selectric typewriter keyboard was even more exaggerated in this regard.
I'm not a gamer, but I guess gamers do a lot of high-impact "typing" and have a lot of nuanced mech-keyboard characteristics they look for, related to impact, sound, simultaneous key-presses, color-coding, backlighting and so forth.
I can get used to laptops with limited key travel, because some laptop-manufacturers have gotten pretty good at working around a short-key-travel specification for ultra-slim form factors. But I much prefer mech keyboards now that I am writing a book. I have a rehabbed IBM PC keyboard from the 1980's, as well as a couple of modern mech. keyboards. The rehabbed IBM keyboard was $275 a couple of years ago, but it is worth every penny to me. The original IBM PC keyboards have a buckling-spring key switch that is different from modern mechanical key switches, and it is one that I prefer. The IBM keyboard is built like a tank, and will last for decades (if I live that long).