~10 years ago I ran the gamut on keyboard layouts during a slow period at work. I discovered a few things:

- Mentally switching between layouts is (surprisingly) far easier for me than e.g. switching between mouse, trackpad, and touchscreen inputs between devices. Most of the time I don't even realize I've done it I just start typing in QWERTY on other people's computers. I don't think I'm super human I think it has more to do with the next item

- About 95% of originally "learning to type" seems to have been unrelated to the learning the keyboard layout or shape of the device. If I had to guess most of it must have been learning the motor skills of how to position your fingers over a dense input device without having to actually think, look, or focus on doing so.

- Corollary to the above, if you learned incorrectly (e.g. you're reaching between sides of the keyboard and you go to use a split keyboard where you can't do that) relearning that alone might take as much effort as learning a new layout.

- My hands stopped hurting even if I spent the day typing on a laptop keyboard. This was definitely the biggest gain for me.

- The quickest way to pick up a new layout was to just cut over cold turkey having a layout reference handy for only the first ~30 minutes (otherwise you spend more time looking at the reference because you're only 90% sure instead of pressing the key and becoming more sure). If you honestly do a hard cut and make an effort to type as long as you normally would have you can be quite proficient again within 1 week and just as good as you were QWERTY within 2 weeks. For reference when I started I thought it might be a multi month kind of process to get to parity.

- Spending a month or two on a non QWERTY layout I was a better typist (both accuracy and speed) on the new layout but the gains in this regard were not much more impressive than spending a month or two practicing typing. I.e. getting to the same speed will happen quick but not because eventually you'll type at twice the speed just from a layout change or something.

- You will never "forget" the commonplace layout (in my case QWERTY). Apart from other people's computers your BIOS, VMs not configured for you, some types of remote sessions that use the server's layout not the client's, certain poorly coded games, and probably some others I'm forgetting will assume you are on QWERTY. Thankfully because of the above this is not a problem, the hard part is typing 5 characters you have to delete once you realize it's QWERTY.

- Corollary to the above: there are keyboards that allow you to set the layout in hardware fixing things like BIOS or remote sessions. It's great outside the game use case where poorly coded games scan for letter but it's the physical positions of the keys that matter for the user resulting in e.g. your wasd being all over the keyboard. Some have a switch but it's usually not easily flipped like a software layout hotkey.

- Other layouts were a bit like a bike, I forgot them after a few months but going back to them was a matter of days not weeks.

- As far as noticing benefits it didn't really matter which layout I used as long as it isn't QWERTY.

These days I really only use Carpalx and QWERTY and I honestly would have been happy with <anything I tried> and <QWERTY>. I also stopped caring about special keyboard hardware as it just seemed like unless I was going to carry my keyboard around with my laptop bag I wasn't really spending much time with a keyboard I could pick anyways (and ones that fit in laptop bags weren't all that great).