Require user signin setting - can anyone find my app or only people with a link?

[Dishdosh]

I got a message saying I need a Pro account to require user sign-in. A few questions:

• If I don’t require a sign-in, what does it mean? That someone with a link to my app can access it, or that my app can actually be found in a search or a database? That’s a huge difference
• The Appsheet pricing page says “Start building and testing apps with up to 10 users for free”. My app will be used by 3 people max. Is there a way for me to require user sign-in, or possibly send it to 10 friends and then any more users will be blocked?

P.S.
It’s totally not cool that it isn’t mentioned anywhere that this is a Pro tool! In the Appsheet console, there are tools that say they are only Pro tools, so I didn’t use them. I got this message after a few days work on my app, very frustrating.