That's very useful feedback, thanks!
Currently, Spectre autofills fields on iOS using iOS' built-in auto-fill capability. The way this ends up working for two-step screens is that on the username/email screen, you'll be offered to autofill your username and on the password screen, you'll be offered to autofill your password. Usually you can do this with a single tap to fill in the field.
I believe when asking the question "what can the site URL field be useful for?" we need to think about how you open the site in the first place. Do you:
- open your web-browser and go to the site, and then use Spectre to fill in your password, or
- start by going to Spectre and tap your site to open it?
We don't really need a site URL field for  but for  the site URL field can be useful to open the site up to the right starting page. What would be your preferred usage flow?
Any other uses we can think of for the site URL field?