This message is not a pleasure for some advertisers at all. Apple has made a small but significant change under iOS 11 at the Safari browser. Thus the reading mode can be switched on permanently - per website or in general. Advertising is often no longer displayed.
The Safari read mode is handy - especially on web pages that are not designed for mobile viewing. If it is activated, unimportant elements are hidden and only the text, images and links are displayed. But if you click on a new link, the normal mode is activated again.
With iOS 11, this changes, which can then decide whether the reading mode, which is intended to deflect the user less, is activated by default. If you want, you can activate the permanent reading mode for the current website or have it activated on all supported websites. That works by the way synonymous under macOS High Sierra.
Although the navigation does not work anymore, iOS 11 is still in beta and is not expected until September 2017. Apple also forbids the browser to play videos automatically. This should also provide for less irritation.