How long did it take you to get as proficient with it as a regular keyboard?

It’s pretty easy to type on one out of the box, but it takes a little longer to get comfortable with layers. The nice thing is that vial makes it really easy to remap keys so you can experiment easily. Moving shift keys to the thumbs was one of my first changes, followed by moving enter to the left pinky (most layouts have enter on the right thumb, I changed it to backspace). Then I wasn’t sure what to do with parentheses, so I got comfortable with space cadet shifting (parens on tap, shift on hold). You can make it a gradual process, tweaking only a couple things at a time, and then the changes feel easier to manage.

Do they have mechanical kinds?

Almost all split keyboards are mechanical, as far as I know of. I use Gazzew Boba silent switches and love 'em.