Google has made it apparent that websites who prompt you to download a mobile app could be punished. They recently announced that as of November 1st sites with "intrusive" add downloads will be penalized:
“After November 1, mobile web pages that show an app install interstitial that hides a significant amount of content on the transition from the search result page will no longer be considered mobile-friendly.”
This is a significant impact to not be considered mobile-friendly because Google heavily favors mobile-friendly sites in mobile search. The mobile-friendly testing tool has been updated so it will warn you for this potential issue.
History has shown that when Google issues a recommendation it's smart to abide. Usually an algorithm update soon follows including that previous recommendation.