[butterbox]

You can setup DNS on the box to redirect users and to give a friendly name to your box. That's what we do for butter box (https://likebutter.app/box/). To make it a step easier, we provide a QR code. But even that is a little clumsy since you must first connect to WiFi, then scan the code.

Captive portals sound nice until you find out how limited they are -- a lot of styling, JS and browser features are simply unavailable. So, you need to tell users "Close this, then go open this site in your real browser"...

Of course, you can't and probably don't want to redirect HTTPS traffic since you don't have the matching cert for e.g. https://google.com