The iOS internet check option is a recent addition to the GIS firmware.
iOS devices, like many other modern devices, have a function whereby they recognize being behind a captive portal and will open their 'webview' app at a web-page to allow for the redirection and automatic display of the required login page.
With older versions of iOS, users found problems with this function where if, for whatever reason, the user closed this 'webview' app, they would not be able to access the network and the iOS device would disconnect itself. This caused a lot of problems for many captive portal providers, and as such a fix was put in place to block this.
When blocked (on iOS devices) the end-user would need to open their browser at a http page to allow for the redirection to the login page (http rather than https as it is not possible to redirect from https without resulting in an SSL certificate error).
Not ideal, but it seemed to work.
More recently apple has improved its captive portal recognition, and seems to work without the aforementioned issues. Similarly a move towards use of https over http, means that many users, upon opening their browser, would not be redirected to the login page causing further problems.
As a result of this it was deemed that allowing the iOS internet check feature provides a better user experience.
We recommend 'unchecking' the iOS internet check option, unless users seem to be having problems with it.
Essentially, disabling the iOS internet check allows iOS users to automatically see the login page when they connect to the network.
If, in the past, you have also been advised to add "www.apple.com" to your Allowed IP list, please remove this. This was another method used to prevent iOS devices opening their 'webview' app and is no longer needed for the reasons stated above.
If you have any further questions about this, please open a support ticket here.