Which of the following metrics would be most relevant when evaluating app promotion effectiveness?

When assessing the effectiveness of app promotion efforts, the most relevant metric is app installs. This is because the primary goal of app promotion campaigns is to drive users to download and install the application. The number of app installs directly reflects the success of the advertising strategy in attracting new users and expanding the app's user base.

Evaluating app installs provides clear insight into how well the promotional efforts are resonating with the target audience. It indicates the appeal of the app and the effectiveness of the campaign in converting viewers into actual users. Without a high number of installs, even if other metrics such as engagement are strong, it would suggest that the initial promotional efforts were not effective in driving users to take the crucial step of downloading the app.

Other metrics like cost per lead, landing page views, and custom events can provide valuable insights in different contexts but do not directly measure the core objective of app promotion, which is to achieve installs. Cost per lead might indicate how economically viable a campaign is, while landing page views can reflect interest but do not confirm that users have completed the key action of installing the app. Custom events might show how users interact with the app post-installation but are not relevant for measuring the effectiveness of initial acquisition strategies.