I am working on the computer on a daily basis. I try not using my mouse at all, so I really use my keyboard a lot. I used to not care about what keyboard I use at all. One day a colleague recommended a mechanical keyboard so I got one for the office.
To be honest, I liked that keyboard and since then I hated the really cheap ones, but I thought about what makes a keyboard good for me and that is typing speed and the duration I can use it without my fingers gettign tired or becoming slower.
So I measured my typing speed (450 keystrokes/min). I then had to use my Macbook keyboard on a trip. After a week I was able to use that keyboard as long as I wanted and my speed was exactly the same as on the mechanical keyboard.
I tested that on several other keyboards as well and after about a week of usage, it makes no difference (fore me).
I am now using a cherry chiclet keyboard, beacause it is very quiet.
I know I am not a very fast typer and maybe it makes a difference if you can hit 550 or 600 keys/min, but for me a mechanical keyboard makes no difference.
I don't know that a mechanical keyboard would make a huge difference in speed: I can find more keys without looking, and I never have questions about "did I hit that key or not?" .. so that must help speed things up a BIT. But as far as sustained typing speed, it's probably not a huge difference. My typing scores have not changed materially in 20 years, regardless of keyboard.