How would you change it? A slider would be worse for this setting.

Ever try to use a slider in a password manager to determine the length?

Trying to set your password to 21 characters? 20… 22… 20… 24… 18… ah fuck it, I guess my password is going to be 18 instead.

When you have a hard limit of 1-30, on a setting you touch once, if ever, this is fine. A text field with the ability to input a number would be okay, except it would confuse people who want more than 30, and that’s bad UX.