How public is a public shinyapps.io app?

If I deploy an app to https://myusername.shinyapps.io/my-complicated-app-name/ and leave it as "public" so no authentication is required, I know that anyone who knows the URL can access it. But realistically what is the chance of it being visited by accident? For example, are there any bots or scrapers that will find it within minutes and post it somewhere? Will it be indexed by Google? Or will it only be visited by someone who deliberately types in the address or clicks on a link that has been provided to them.

The use case it that sometimes I want to test an app with non-trivial numbers of people who I don't want to force to get shinyapps.io credentials. Leakage of the URL would be annoying but not catastrophic, so I'm wondering what the realistic risk is of just having a public app and sharing the link.

I don't think it's easy to answer your questions - how would R shiny users or sustainers know?

Seems to me there is undefined and not insignificant risk when publishing shiny apps using methods without authentication. Especially if your username is known, then other apps you have published may be relatively 'easy' to find.