The vertical monitor is 19" which seems like it's about the right size. It's long enough to give more vertical space but not so much that it's inconvenient, as in having to scroll my neck a lot up and down to scan the monitor.

It's been really helpful for using Google Chrome's Inspector tool. That's usually on the vertical monitor where it's easy to modify the CSS and then notice the changes in the browser on the main monitor.

And doing this without having to switch apps helps.

It didn't seem that switching apps took up a lot of time. But since switching to the new setup, making changes to code seems easier and goes by more quickly.