All keyboard layouts can be customized in software but some keyboard hardware like QMK can be programmed in hardware, which makes it especially convenient for switching computers.
Where do you use it? Do you have to use different computers at work or do you just carry your keyboard with you all the time in case you have to use some friend's computer?
Keyboards like Keychron are able to store BT connection info for multiple computers. So, you can easily switch between, say, your desktop, your server, and your laptop, as needed. Or bring it to work, or whatever. The point is that being able to use the same high quality keyboard with every device is nice if you do a lot of typing.
I had a quick look and yeah, $100 for a good, wireless keyboard is not that much. It definitely happened to me once or twice that I had to type directly on my Raspberry Pi fresh after installation when I didn't have my key mappings set up there. Other than that I just switch single USB cable between two computers on the same desk and that's it. If I ever have to work on a Mac again I will take another look tough. Do they have Linux software?
Maybe. Or maybe it is one of those things that you think you don't need until you start using one, and then you can't believe you waited so long. :)
Portable wirless mechanical keyboards are niche, but not uncommon. I bought a Keychron for my daughter and she loves it, though admittedly I'm not sure how often she uses the ability to move it between computers.
You can also connect it to your phone, so you can use it for portable long form writing or programming with just your phone or tablet and keyboard if you don't have a laptop. I'm sure it is better than using the Surface keyboard, for example. Many laptop keyboards also suck, especially if they use an ISO standard keyboard when you already have muscle memory for the ANSI layout.